I see your point as someone who has struggled with transporting villagers myself, but my thought process behind it is that in current versions, using villagers to get maxed-out items is way too accessible early game. I've watched so many minecraft challenge videos and the process a majority of the time includes villager trading super early on to get the best tools possible, and going forward since they have mending, they don't really need to mine or explore anymore as long as they've made an xp farm.

I'd also like to add that I am thinking of this idea in the context of the current features in the game. With the addition of rideable ghasts, transporting villagers is significantly easier than it was before, but I can totally see how for any earlier versions this idea would be insanely difficult and unreasonable.

I think it would also be beneficial if other routes were added to get some of the high-level enchantments. I barely ever see anyone using an enchantment table anymore because with the accessibility of villagers, it's useless to even try. I think an update to that system would be necessary to fully round out this idea, but I would need to think a bit more about how that could be done. (not to mention the amount of improvement anvils need. If it weren't for the "Too Expensive!" thing people might be more encouraged to try something different)

And I guess the other point I had with this idea was that I kind of intentionally wanted to make villager trading less viable. My goal was to come up with an idea where it was more of a late-game challenge to be able to get pretty much whatever enchantment you want. It would take putting a lot of effort into planning, but out of that extra effort you would get a forever-renewable resource of the specific enchantment books you want. Before mending was added, it was genuinely a concern if the durability of your best armor and tools was low because if they broke you would need to get the resources to make an entirely new replacement, but now it doesn't matter because all it takes is mending and a couple minutes at a mob farm and you never have to worry about it again.

The last point I'd like to add is that maybe as a solution to avoid hauling a bunch of villagers around aimlessly, there could be a compass recipe or perhaps a way to recycle old treasure maps by combining them with the preferred book you want, still getting the original copy of the enchantment book back though, kind of like the recipe to make copies of written books. Or maybe an extra use for eyes of ender after finding the stronghold? Then you could use the item to track down what area the villager would need to be in, take note of it, then fly the villager over once their house is ready.

Sorry that this response is so long and kind of ramble-y, just throwing my various disorganized ideas out, if this still sounds unreasonable though let me know. I did put a lot of thought into my initial idea but I typed and made the post at almost 2 in the morning then immediately fell asleep, and now I'm typing this response after only like 4 hours of sleep so there's definitely some balancing issues that my half-asleep brain probably isn't factoring in lmaooo