Really difficult to say - then again, upgrading from HD to 4K / 8K territory might not be in Nintendo's best interests for the next console generation. If they wanted they could work up to 1440p (the middle ground between HD / 4K) and go from there really. Not a huge jump, but it would still be rather noticeable on a large TV. If Nintendo decides that not enough people have 4K / 8K TVs to begin with, they're in a similar situation as they were in during the Wii era -
when HD TVs were publicly sold, but were not yet in enough peoples' homes for Nintendo to feel confident. So I could honestly see a situation where they don't upgrade the graphics that much but instead focus a bit more on performance.
I'm not entirely sure why they had Brawl Zelda transform into Sheik, might be due to Sheik's relative popularity back in Melee + some of their aspects not working as intended and them wanting to fix that with Brawl. Lets look at
Sheik's Melee Adventure trophy:
The intent with the design was to have Sheik be the
of the couple and Zelda be the
(to simplify). Which makes quite a lot of sense on an intuitive level - but could pose some design problems if they were to implement Toon Zelda and include Tetra / Toon Sheik (might've been a key reason why she was dropped).
The main problem with that though is that Sheik / Zelda are diametrically opposed: a person who does intuitively well with Sheik or Zelda is not likely to do well at all with the other since their strengths require effectively two different mindsets. Also, this:
Turned out to not be the case in Melee (likely due to time constraints meaning they couldn't entirely playtest), which severely undermined Zelda or the need to transform:
Sheik's F-Air is an infamous test case since it was a semi-spike bitchslap of death. Sakurai and co. intentionally nerfed it in Brawl, then repurposed it entirely into a combo move by the time 4 came around (in favor of introducing Bouncing Fish and turning the Smash attacks into the kill moves).
Didn't help that Melee / Brawl Zelda and Brawl PT had some character-specific jank that harmed them: Zelda's incredibly unreliable finishers in Melee and Brawl - an area she was supposed to excel in according to
her Melee trophies - Sheik likewise had that same weakness in Brawl, Ivysaur's weakness to fire in Brawl, character swap being slow in Melee and incredibly slow in Brawl.
Think that decision to split Sheik from Zelda came around because it's really difficult to design a transforming character in a way to encourage people to actually switch between the forms and not just stick with one over the other. Now this is not a Smash-exclusive problem in the slightest, but it is relevant to Smash since 4 was also the game where Zard went solo and PT was nowhere to be seen. So I'm feeling decently confident saying that's one reason. And it wasn't until Ultimate where they found solutions that would at least minimize the problem.
While no solution is ever going to be perfect, I should take this moment to commend Sakurai and co. on how they handled
and
/
in this regard. Those designs make sure to actively encourage switching because the character strengths / weaknesses are consequential yet not overbearing: PT allieviates possible barriers by having some overlapping strengths (Ivy and Zard can both kill reliably, Squirtle and Zard can react very well to opponents' actions, Squirtle and Ivy have both good grabs and advantage), Aegis have the least barriers due to being semi-clones, Sure, there are and will be people that stick to one form, but still.
That doesn't look too much different from say
's Mach Tornado - which travels a lot horizontally and can get some vertical distance via mashing, but renders him helpless after and can bounce off of edges if one is not careful - so it should be fine. Sure, it has quite a lot of coverage and could be difficult to intercept (except from the side, akin to K Rool's Copter) but I could certainly see BWD having multiple midair jumps + the Copter.