Strange Ending: Heatran gets some sort of counterpart, or like an underwater volcano-themed regional form
Personally, while I do like all of those additions, I kinda hope the Tapu are left out of it. Maybe this is a take for the unpopular opinion thread, but I’ve always preferred to have some level of imbalance when it comes to the distribution of things like evolution and forms and such. Or, maybe not “imbalance” per se, but I don’t think it’s a bad thing to leave some things untouched.
Like Dragonite. People talk about how it has unfortunately missed the boat on Megas, Z-Moves, regional forms, Gigantamax, etc. generation after generation, but all of those missed chances give me a sense of the original pseudo-legendary standing the test of time. Good ol’ Dragonite just is what it always has been, and doesn’t necessarily need to change.
I guess in my mind, when everything has some sort of gimmick or variant or offshoot, it just starts to feel like something being done out of obligation rather than as an organic choice. Of course, that’s not to say I think parity should always be avoided. I think it would definitely feel weird at this point to give, say, only some of the Eeveelutions a Mega Evolution, or what-have-you. They’re such a closely knit group that disparity in their case would feel more like exclusion. Whereas things like “pseudo-legendaries” or “minor legendary trios” are broader and less intrinsically linked, so them not all sharing the same creative paths makes sense to me.
(Funny enough though, I’m a tiny bit of a hypocrite here because, as you note, the Lake trio weren’t really revised in terms of design, but part of me wishes they had been, if only because I’ve always felt like they’re very same-y. The Forces of Nature quickly rectified their lack of design variation with the introduction of the Therian Forms in B2W2, and I sort of always wished that would happen for the Lake trio. Even more so in light of Legends: Arceus giving them each a related key item with a rather evocative name — Uxie’s Claw, Mesprit’s Plume, and Azelf’s Fang — but alas, I am willing to settle for them being one of the few “untouched” minor Legendary groups.)