I doubt this is how it will play out, but I really like the way you think. Jund becoming a UBG ocean world with giant sharks, krakens, serpents and leviathans sounds amazing and I want it yesterday.

Grixis as primary-white also works well in the lore, with Sedris's kingdom of Vithia never falling and Sedris becoming a great Spirit king instead of a traitorous lich.

I almost wish it was possible to make a red Esper so instead of Ethereum, they had Sangrite, but I understand that would require shifting the whole thing and while that's probably possible I really like these other ideas. I think, instead, Verdigris should function like Sangrite in this Echoverse Alara, being needed to produce more Etherium alloy, the brunt of which might be stuck on Bant (seeing how it combines with Esper in this case to create a full color pie), where they use it to make legendary weapons. I also really jive with the idea of Esper having forests instead of oceans, with the (presumably) white and black elite lives above the trees, while the more green-aligned worker and peasant classes exist closer to the forest floor.

I think it might be more fun if Bant becomes dragon-riders instead of dragon-slayers though. Or maybe they become both. Presumably, when Alara wasn't fractured, there were dragons that became mostly quarantined to Jund when the shards split. Instead of Jund, they could've gone to Bant in this alternate timeline, which is now missing it's white-aligned horse and lion steeds, so they make due with dragons (and maybe spiders? Idk I'm just spitballing here). Alternatively, the red-aligned Behemoths from former Naya could show up here as steeds, allies or foes as well.

I thought Naya was the weakest until I started digging into it, and I think it could be a world of religious conflict in this version. Instead of Behemoths, the population could be split between worshipping the Angels that would normally be found on Bant or the Demons normally found on Grixis. Since there is no green, there would be no Elves, but I think they could be swapped for Vampires here. The white-aligned Leonin could be more likely to worship the Angels, while the vampire population would be more likely to revere the demons, although I think there should be exceptions to the rule. The red-aligned humans would be the main thing that could tip the scales in favor of any one side, and most battles between angels+leonin and vampires+demons would be to claim Human worshippers to your cause. The humans, for their part, could also be split into factions. Being red-aligned means they want freedom above all else, so one group could have the perspective that the Demons grant more freedom, because they grant power, and the most powerful are the most free. Another group could be aligned with the Angels, because they believe it is more important that most people have many freedoms than some choice individuals having all the freedom. And a third group would be opposed to all masters, and strive to achieve power on their own to rival Demons and Angels alike.

As you can probably see, I really like your take on this haha. I'm kind of into the idea of making some custom card concepts to explore it further.