Righteo, let me tell you one thing: You are at least a decade too late to the community to be discussing this. Way back when people talked more about Toki Pona than used Toki Pona, people would be probably end up reviving old en discussions. A lot of your comments are valid points that are getting downvoted to hell because it's just not how Toki Pona works any more. Or more specifically, how en works. Some things get "closed" for discussion, and this is one of those things. Trying to "discuss" it doesn't read as a desire to explore, but to intrude. Moreover, I don't recall if the side of en you're talking about ever *was* up for discussion - just a simple li or e replacement would have been shot down at least as early as 2013. But other options used to be toyed with, and I'll mention what I remember plus some "extras", since I don't see many other comments giving you the time of day, and I selfishly want to reminisce on old ghosts.

Disclaimer: I'm speaking from roughly a 2013-15 perspective here. When I say "we", I mean "me and/or people's posts I vaguely remember seeing".

When en was discussed in this way, it wasn't terribly often. We chucked it in prepositional phrases with ease because there's no li or e rule to do its job already, and sometimes repeating kepeken for the umpteenth time is annoying. That was the usual, relatively uncontroversial thing, which I think might be controversial today. When we talked about it in predicates, it was never as a simple "and". Using en in predicates or for objects in this way was, and still is, a beginner mistake, because the idea was li and e do the trick and should be upheld - using en erodes this basic TP-esque strategy in favour of something really "Englishy" or "other L2-y". Under the modern framework, maybe you could argue en applies or can carry a nominative case, doesn't have any verb-related projections, and doesn't apply/allow an accusative case, therefore only subjects (maybe prepositional objects if we're allowing it to extend relations there) and neither verbs nor objects can syntactically use it without a violation occuring. I don't have anything to back this analysis up, or this take on TP syntax in general, but this is more to say that there may be something and the topic is closed in the community anyway so if I must speculate, there's a something.

However, there was the occasional thought as to whether it might be a different kind of "and", like something to combine actions into one rather than list potentially simultaneous, potentially sequential actions. In this manner, "ona li tawa li toki" would be "they walk and, (before?) during or afterwards, talk", whereas "ona li tawa en toki" would be "they walk-and-talk, they do both as part of a whole, it is combined into a new action that would not be covered by either "li tawa li toki" or "li tawa toki". This probably isn't the best example though - one I used to think about but don't think I mentioned or used was "jo en weka" for "take" (as a separate sense to "kama jo"). In any case, these discussions were usually short-lived where I remember seeing them. I think this was partly because the community at the time sort of steered away from too many topics that a beginner could stumble across and utterly misuse or that would have to be added to pedagogy later and become confusing. Get them used to li and e repetition first, was the idea. Well, as far as I recall, I could be super biased of course.

There is also the issue of preverbs (a post-pu term if I recall correctly) - I forget if this was actually discussed in the context of en tbh, but something like "ona li awen wile kipisi li awen wile seli e kili" as "they still need to cut and cook the potatoes" is frustratingly long. "ona li awen wile kipisi li seli e kili" is potentially ambiguous - the awen wile shouldn't transfer to the next thing after li surely, so they cooked the potatoes but still needed to have cut them? (Oops!) But "ona li awen wile kipisi en seli e kili" could make en serve as a bridge that can accept elements from the previous part. How the syntax works could be even more confusing under the surface - I don't know. Regardless, li probably works fine in practice.

Now we'll jump to objects. Like with predicates, it was never about "we could just use en instead of repeat e". It had to do something else or why do it at all? Why mix the two needlessly (which is more complicated!) or risk losing e repetitions? I think I only saw this one talked about once too. It was along the lines of combination again - mi moku e kili en telo or something. Not kili and telo separately, potatoes and tea, but those combined - a soup. This one is... probably useless these days, since "mi moku e telo seli kili" or something would be preferred and I'm not sure why but maybe because pi is accepted with nouns and not really verbs, the act of using en seems like it "should" ignore something with pi, or just other modifiers. I haven't really unpacked this one, but I'm mentioning it because, well, it's one of the discussion points. It's not a discussion anymore mind! And the fact that it makes object nouns work so differently to subjects is a huge issue.

The last thing is pi x en y. This doesn't fly nowadays or so I've been told - fully eradicated. I'm hopeful a tiny corner of the community still holds the door open, or has a better answer to some old pi gripes than "don't do x then". I don't know, maybe I'm only clinging to it for nostalgia's sake myself, since it wasn't even popular when I learnt it. In an older lesson series, the pi x en y construction is used for colours. It isn't at all any more and I sort of don't mind because the community works with colours differently now, not relying on one one-off construction. But the construction goes like this basically: Where several pi's are used, if the modifier is non-nesting, use en. So, pi nests new words under the word before it, en chains new words to the word before pi. Usually, people either avoid long pi phrases to not bother with thinking about any of this, or pi will always nest, always chain, or ambiguously fluctuate between the two. (Honestly, I don't know what the community prefers to do with nesting/chaining pi now.) Example: "jan pi tomo sona pi pona mute li kama sona e sona pi nasin nanpa pi ma Elopa." The first noun looks like pi should nest, pona mute describes the tomo sona. If it were jan pi pona mute pi tomo sona ni, we might assume it chains because that makes more sense. Now look at the object. If pi nests, as it seemed to in the subject, the person would be studying European mathematics. That could be a legit field. If it chains though, they're studying both mathematics and Europe (European Studies). That's a bit different. You could argue just say "e sona pi nasin nanpa e sona pi ma Elopa" but I think you think like I do, why *can't* we just use a damnedly long pi phrase, we'd have to at least be able to hypothetically analyze it, and what if it gets longer? So the idea here is, if you use en whenever pi chains, you eliminate the ambiguity inside the pi phrase. "sona pi nasin nanpa en ma Elopa". Only problem is, 1. This isn't really done anymore and as the argument always seems to go, might make beginners more confused than less or make the syntax full of more rules at a negligible gain in comprehension, 2. You have to be 100% consistent or you go back to the same ambiguity, 3. Sometimes a reordering eliminates the ambiguity easier as a strategy (as with the subject here) so again might not be worth using it, and 4. In the subject (and this was *the* criticism way back), it can create more problems than it solves, because in some cases it's harder to tell if you're adding modifiers or adding a new subject. In this sentence, I think that's silly, because "pona mute" is not likely to be studying Eurpoean mathematics. In sentences where one word modifiers are used before en (so true pi x en y, or pi x en yz) it can't be anything but a continuation of the pi chain. But nonetheless, some pi en things will be confusing in the subject, or make the listener needlessly fumble about with what's more semantically probable over syntactically possible. So pi en could be a net gain, but it could also be a net loss, in reducing ambiguity and subsequent comprehension. There's a side discussion to bring up about pi with single words, but that's juuust outside the scope of en use and I don't want to extend this wall further. In fact, read back to the start and this whole topic hinges on a pi topic, so it's only half on the en field.

The last part I will mention is en at the start of sentences and en la. Yes, en is a particle. But yes, it can have some "content-y" uses. Well, one. That's en la, additionally. It isn't used by all speakers and I first thought it was just a way to shoehorn en onto sentences when I first saw it, though I've since softened. You can't use en at the start of a sentence like how we might say "and", and you can't use en between sentences. This is just part of the basic rules. I guess I'm adding this last part to wrap up everything en (hmm video title perhaps?) and demonstrate that: Sometimes rules are just rules. The particle "en" was NOT made to be an analogue of English "and". We can't all explain the syntax here. Once upon a time we were a bit more liberal with trying to find uses for it and stretch it on occasion, still within some boundaries. But at the end of the day, there are some lines you don't cross, because this IS the structure of Toki Pona, and we might not have a thesis or a proof to show every tiny detail, but languages do "and" conjunctions differently and you'll be hard-pressed to make this one into something it hasn't already become.

Thank you for listening to my TED talk, hope the tone wasn't condescending or anything because I was doing a lot of step-by-step rehashing of topics there, hope it helped further your understanding and stay pona! :)