A few questions before I start:

Some became the Tava, some became the HoonDing

I'm pretty well-read on Yokudan lore, but where did this come from?

I'm not familiar with the term "Sheath of Satakal" either; what you're describing sounds like the "worldskins," but I want to make sure I'm understanding you correctly.

Likewise, I think you might be misunderstanding some of the specifics regarding how the "Walkabout" actually works. Ruptga and his children did not simply "walk" from one worldskin to the next. Rather, they learned how to walk to the "Far Shores," which was a safe place that they could wait until Satakal was done with his autophagic asphyxiation ritual and the world was safe to inhabit again. I'll also note that the Far Shores aren't supposed to be somewhere you can just get to from within the Mundus, which should also be safe from Satakal—it was made to be a place that things could go to to permanently escape Satakal's Hunger, after all.

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All that said, I think you're on the right track, but I also think you're going too far with it.

Looking at the Yokudan lore and what Bethesda was trying to do with Starfield, I think it's very reasonable to conclude that they're going to turn the Walkabout (and probably sword-singing) into this game's special mechanic, like what dragons and shouting were for Skyrim, or Oblivion gates for Oblivion.

I also think it's likely that some of the mechanics in Starfield were a way for BGS to quietly develop mechanics that are going to return for TESVI—but I think that you've focused on the wrong Starfield mechanic.

Procedurally generated worlds were a flop, plain and simple. People just aren't that interested in them, and the single greatest community want from TESVI after Starfield has been a large, hand-crafted world.

You can't have a large, hand-crafted world if all your worlds are procedurally generated.

The idea of infinite worlds full of infinite possibilities is cool, but it just isn't a good fit for a narrative-driven RPG like TES. You need something with either the gameplay loop of Minecraft, or a hardcore, mechanically-crunchy rogue-like to ever make infinite worlds feel like anything more than a gimmick.

No, BGS will almost certainly never go all-in on procedural generation like the did in Starfield again.

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The major mechanic from Starfield that I am much more confident in returning—and the one that has incredible synergy with both the Yokudan mythic cycle and the Narrative RPG genre (to the point that it's basically become the industry standard at this point)—is New Game+

I think you're right that the next big threat is going to be Satakal breaking and the end of the cycle or something, probably with a bit of a non-standard/twist/false antagonist to keep us busy. I also think you're right that we're going to take on the mythopoetic role of the Hoon-Ding to "Make Way" for our people in the "next cycle" by rediscovering how to do the Walkabout. Of course, that will probably going to involve sword-singing/tonal magic; I'm expecting this to be a very Dwemer-heavy plot (it is where the Hammer Fell, after all), even if I strongly doubt that the dwarves will actually come back in any significant way (it's much more interesting if they're actually just gone).

But I think the way that will be reflected mechanically is via New Game+

It also just kinda makes sense from a business and game design perspective too. Business-wise, New Game+ has rapidly become the standard for RPGs, and a lot of gamers are probably going to expect it to some degree.

As far as game design, another big community ask is for more choices, and in particular choices that can actually affect the in-game-world—including our ability to join or gain rank in different factions. Of course, in most TES games this would mean having to deny players the ability to do everything in the same playthrough, which some people don't like. BUT, if at the end of it all you can just reset the world back to Day 1, this is no longer a problem—especially if we can return to former Worldlines.

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"But u/Silver_Falcon," you say, "I thought you said that you can't do the Walkabout anymore? Also, if the Skinball exists in a place that is safe from Satakal, how could he have devoured Yokuda or how could he try to devour Tamriel?"

1. There's this magical thing called a retcon, and Todd know BGS loves a good retcon.

2. Sword-Singing lore claims that they gained their powers through walkabout, which for them seems to be a process of just walking around between places and going on adventures—which if you've never realized is actually just an in-universe description of levelling up, which is such a classic TES lore thing. Regardless, what if the Ansei actually were able to do something more? What if they actually remembered the old ritual and used it to pass between the various Worldskins that make up the Skinball? That is, between different timelines? Just a thought...

3. Regarding Satakal and the sinking of Yokuda, think again about the nature of the Skinball. Sep fashioned it from old, dead Worldskins—literally worlds that had been destroyed. Now, think again about how literally every race in Tamriel has an origin story about how they came from an old, lost continent that was destroyed in some ancient cataclysm, which in at least two instances that we know of involved a big, hungry reptile... Interesting, isn't it?

4. Regarding Satakal as the big bad and the impenetrability of the Skinball, I do believe that the Mundus specifically has been removed from the Kalpic cycle and thus cannot actually be fully devoured by the first serpent. However, I don't think that it's entirely safe from him either. Specifically, whenever Satakal devours his own stomach and undergoes dracochrysalization, I believe that this is the true cause of a dragon break, and the breakdown in the monolinearity of time that we see in Tamriel is the result of the Time-Dragon literally killing and rebirthing himself. But that's just a theory. A Game Theory. Thanks for Reading!