Doesn't really matter if there's loud backlash or not. It might simply be all what we're getting. And for a dormant franchise as Golden Sun, it's even more than many would expect.
I am not sure if DLC is even going to include first or second party characters anymore. I don't even have high hopes for a Three Houses Fire Emblem character, or a new Pokemon from Sword and Shield. In fact, they might think these franchises have enough characters already, which is a honest and fair point all of it's own.
I might sound pessimistic with that, but I do think there's potential for the popular ATs in Ultimate yet. Considering how many of the newcomers of Ultimate got major upgrades from last time, I do think that the current popular ATs are front runners for newcomers in the next game, if there's even gonna be a next Smash game with a roster as huge as Ultimate's (personally, I think we can expect at least 25-30% of the current roster cut).
Now the examples of newcomers who got a huge boost to playable status from their Smash 4 incarnation:
: Stage boss on Pyro Sphere
: Assist Trophy and alt costume for Samus
: Assist Trophy and Mii Costume
: Mii Costume to throw the fans some bones
: Weirdly enough, still part of
's Final Smash and straight up denied from playable status due to not being unique enough
: Was a alt costume to
ever since Peach came into Melee
: Mii Costume for the Gunner
Well, look at that, that's basically all the newcomers but
and
. The Belmonts are easy to explain why, Incineroar didn't even excist at the time, and Ken? Well, Ryu was already a DLC character in Smash 4 so having a second Street Fighter character would've been too much honestly.
If there's gonna be another ballot, characters as Isaac, Skull Kid, Waluigi and others are probably gonna be the next most requested. I just have NO idea at all where this gaming franchise is going from Ultimate. It has a huge roster, and seems like the ideal "template" to build future Smash Bros. games around. Just add the modes which Ultimate didn't have, a couple of newcomers and that'd already sell.
With that said, I do think Isaac is pretty safe to expect for a future Smash, if they are gonna build off from Smash Ultimate (keeping the engine and characters exactly like their final patched versions of Ultimate barring possible moveset changes).
There wasn't even as much time in between Smash Wii U and Smash Ultimate's release dates as there was in between Melee and Brawl, or Brawl and Smash 4 3DS, so I do think it's possible that a new Smash Bros. will be made as soon as a next generation Nintendo console is in production.