It's definitely a recent thing. One E3 trailer and suddenly a bunch of people think this character that didn't exist when the DLC was decided actually has a shot.
I mean, yeah. It was at E3 when we learned more about him and his transformation. We already saw him though, and I clearly remember people speculating he could be our SMT rep for Pass 2, but that was a minority and as I said, just speculation. So the whole thing didn't really started after the E3 trailer.
The character has obviously existed for a long time. If by existing you mean "known by the public", then the protagonist was technically known since 2017. We didn't see his face, but he clearly appears here accompanied by a girl.
And people suddenly talking more about him, well it's natural, his game got a big trailer and a release date, then you have people assuming the final DLC will be either a shill pick or not a big name, and SMTV comes soon so it kinda fits.
Though I wouldn't be mad, if anything, just surprised because as I said I'd expect Demi-fiend first, not Nahobino. But at the same time, I don't think he's as impossible as some believe, just unlikely because while timing-wise I think it's possible, it would certainly require some things to be properly aligned, and because there are other options such as Demi-fiend or maybe even Flynn from SMT IV.
But EricTheGamerman probably explained the whole thing better than me:
I think the Nahabino situation is people projecting past Fire Emblem frustrations and general "JRPG Swordsman" fatigue combined with the "Smash doesn't end on a hype pick" ever mentality all in one go and then the usual suspects who saw Hero get in next to Dragon Quest 11 and are convinced that a promotion has to happen.
Which is a damn shame because SMT is one of the remaining JRPG franchises that makes a lot of sense and has the historical context to be a great pick on its own without all of those unrelated feelings causing that type of pick to be panned if it does happen. Like if it does happen (Which I unfortunately doubt out of my own pessimism and Persona forever being the more mainstream brother), that would 100% be the biggest closer Smash has ever had still lol.
I 100% agree with this post.
I understand that for others, he would feel like a shill pick or a bad pick because he's a super recent character and all of that. But I genuinely like him, which is more than what I can say for a lot of videogame characters, old or new. But let's gonna be honest, even if they went with Demi-fiend or another SMT protag that isn't Nahobino, most folks would still complain or consider the choice as a shill pick because the series has a new game coming out soon.
Basically, I doubt most non-SMT fans really care about who they add to rep the series. The only difference if they went with Nahobino is that some folks would have an easier justification to call the character a shill pick, but they would still do it if they picked a different SMT representative.