So, in other places I've seen the mindset that with the full picture regarding the Mario series' (Paper Mario in particular) diversity and creativity becoming worse the more information is revealed, that now it's time to just give up and 'move on', and never expect anything like the late 90s/2000s again.
I disagree.
This is, to be honest, the time to push back even harder than ever before and find a way to get them to acknowledge that this is a major flaw that is destroying their IP. Obviously I'm not telling anyone to go harassing Nintendo (and I feel like I have to clarify because if I didn't someone would claim that was what I meant) but we need to find a way to let them see and understand - more than simply feedback on their games, but feedback on them as a whole as well as all of their practices. Sure, Sakurai might be able to grab Geno from the void if he wanted to, and Geno might appear in some capacity afterwards, but if we ever want to see a new Geno, or Toadsworth, or Rosalina, ect. then we're going to have to fight for it. And that's a depressing thought. The 2000s hold my fondest memories of video games in general, and I've never forgotten the way I felt when playing the Mario games from around that time - that the little differences in tone and style did nothing but broaden the scope of the Mario series and enrich what was already there in doing so. The Mushroom Kingdom you see in the early to middle Party series feels way different than the one you see in Paper Mario, and the one in Mario & Luigi, and that's completely okay.
I get that wanting to maintain a consistent brand image for the sake of integrity isn't necessarily a bad thing (and can be a very good thing), but let's be honest: nothing that Mario was doing during that period was harmful to the series or 'pushing the limit' in any way. He wasn't exactly whipping out chainsaws and shotguns in TTYD. He wasn't scooping Goombas' eyes out of their heads. He was literally just on a vacation somewhere he'd never been before and experiencing new things right alongside the player - which, in my opinion, is the greatest purpose of video games in general.
I really hope Geno gets into Smash and that his success is enough to make them think, if not 'Wait, they really like that kind of thing?' then at least 'Fine, your interest is stupid but we want your money in the future so we'll do some more of that'. Because I wonder if they might not actually fully understand that people played those games (SMRPG, Paper Mario, etc.) because they liked their qualities, not just because it said 'Mario'. Maybe a DLC character separate from the overall sales of the game where they can see how many people actually purchased that character in particular might be enough.