It’s hard to say what Nintendo will do. On one hand, they pick the characters, Smash 4 ended specifically on a recent characters and we have seen first party titles on the Switch get a nod. On the other hand, Nintendo doesn’t always pick the shilliest option and picked characters like Banjo as much as they picked Byleth and Spirit Events already support recent releases in a way Smash 4’s post-game support didn’t have that.
Three Houses was also a big title, the likes of which we haven’t seen this year. To pick a character from a recent title we’d either have to be much more on-the-edge with the timing and nominate games like Metroid Dread, which release much later than six months before the character is revealed, or go back in time and look at…honestly I don’t know a game big enough that’s more recent than Xeno2 that wasn’t Spirited. Spirits again represent another way to represent what’s coming around. I guess Luigi’s Mansion 3 could count but at that point you’re going so far back you might as well bring in a Champion or something Star Allies if you want people to be able to play as the latest Smash challenger.
In himdsight, Corrin’s inclusion wasn’t a leap of faith based on the knowledge that they’d miss the boat the next game along with the rest of the characters released in a five-year period, but only was one of a select pool of characters that would’ve been stuck between a rock and a hard place for a game that started development the minute they’d be released. Smash Ultimate FP2 might not reserve such a slot because the gap between Ultimate and Gabagool would be more than an awkward gap year so there’d be no huge point in filling the gaps with a specific 202X release in tne same way Corrin was chosen.
Whenever DLC was chosen though, it’s always possible they reserved a slot for something new like they did with Corrin of how base game operates when it comes to Pokémon. It‘d make sense to do so in 2018 when your last character releases in 2021 to cover for the close-to-four-year gap and it’d make sense in 2019 since you’d have a semblance of planning.
Saying that DLC was chosen or decided on early actually helps that imo: DLC wasn’t explicitly announced to be locked in until Fall 2019 iirc, so that final slot could’ve been pencilled in as “Eh, we’ll figure it out” until being locked in once they used their Nintendo foresight to lock it down when DLC was well underway.
Overall, it’s hard to say whether the final slot will follow the way of Smash 4 and fall under the moniker of “Play as the main character of a game you’re playing right now in Smash as well.”
I believe in being pessimistic to avoid disappointment. I've already seen what blind optimism leads to thanks to the Grinch leak.
That and I genuinely believe we're getting a Pokémon, spirit event be damned
I’m hyped for no one, I’d get the same hype for Cinderace as for Crash. I can predict who I want and it wouldn’t get my hopes up. It‘s weird.
