I do think moving on from Ultimate is the best move. Ultimate Deluxe, or bringing back most veterans will likely be an idea in Nintendo’s back pocket just in case, but I doubt they’ll need to pull those cards with a new game.
It is pretty unsustainable to prioritise only the next big thing, the next big franchise to be in Smash, as you likely end up with a barebones roster. We’ve seen Mario V Sonic, Link V Cloud. At some point, it does get old.
That’s why we see a lot of fighting games cycle out old faces for new faces.
The big question is how severe will this change be?
If it’s a traditional new game, I’d expect certain third parties, legacy characters, and fluff from series past their prime and the obvious Mario/Pokémon/FE fluff to be cut first.
That isn’t a guarantee some veterans will never come back.
skipped out on Brawl, but returned in Smash 4. So never say never.
I’ve talked about it before, but I think Ultimate delayed a lot of other Nintendo additions due to its focus on legacy newcomers and third parties. More specifically, who represents Nintendo the best today?
Series like Animal Crossing, Xenoblade, Splatoon, and Pikmin are all primed for substantial roster growth, ingraining themselves into the core lineup much more.
This does probably mean things may work the other way too.
If it’s a reboot, I think some questions are in order. Many expecting a reboot are also expecting more legacy picks to join and return. I think under a true reboot, we will see less legacy franchises than a traditional sequel.