I know this is going to be a controversial statement, but I can easily see them just keeping the current Smash Ganondorf and adding in Demon King Ganondorf as a new character.
I think it is easy for this site to end up as an echo chamber. If I had a dollar every time someone demanded that Ganondorf got a hard rework, I would have enough money to buy Smashboards itself. It is no secret that this site in particular has beef with the current Ganondorf moveset. This is not unwarranted, despite the changes that have been made to him. Ganon sells the fantasy of pure power and they have pushed him into something that more resembles the Ganondorf we all know and love.
And yet, its easy to dismiss that Ganondorf is insanely popular among casual fans. When Smash Ultimate first came out, Ganondorf was the single most popular character online. Not at Elite Smash, but at lower mmr brackets he was king. There is this causal fascination with that pure power motif, an easy to learn bruiser that has crushing power but nothing else. Even when Ganondorf is bad, there is this mythos around him for casual and competitive play. In casual play, he is the crushing tank that will do well in free for alls (depending on the stage) but suffer in a one v one. In competitive play, he punishes you for disrespecting his power while also preying on your fear. It might be a hard pill to swallow, but a lot of people really like the existing Ganondorf moveset.
Is the current Ganondorf moveset a relic of compromise? Sure, it was a last minute rushjob to get a fan favorite character into Melee. Is it canonically accurate to Ganondorf? Not really. While it does sell the idea of Ganondorf being all about crushing power, Falcondorf doesn't really represent Ganon/Ganondorf much at all. I get those criticisms. But I think people kind of let their own biases get in the way of things. If I had the choice during Melee between a Falcondorf and a regular Ganondorf, I would have chosen the latter in a heartbeat. I would like a canonical Ganon, it is one of my most wanted characters/concepts to happen. But I think it's also important to understand that while plenty of folks want that, plenty of folks also love Ganon as is.
I think that's why they have made compromises when changing him up. Giving him a unique F Tilt and Flame Choke in Brawl that come straight out of Twilight Princess was a good start. His new Smash attacks in Ultimate help push this compromise further. There is clearly some attachment on the development team as well as the fandom at large to the Falcondorf moveset, warts and all. I know plenty of folks would want to wash away Falcondorf as one of Smash's original sins, but I think that does a disservice to the far larger amount of people who like Falcondorf.
That brings us to Demon King Ganondorf, hot off the presses from Tears of the Kingdom. We now have a shiny new Ganondorf design central to the plot of a new Zelda game that we can use as a mold to give the fans a new Ganondorf moveset while not abandoning Falcondorf entirely. It is not like having multiple Triforce users is out of the question: we have had at least two links since Melee and have had Zelda and Sheik separate for two games now. I know that the idea of another Triforce user "cutting the line" of other Zelda picks will run sour for some fans. Would I like characters like Impa, Midna, and Skull Kid to rise to the occasion and join the roster? Absolutely. But after five Zelda games where Triforce users are all we have for Zelda newcomers, I feel kind of jaded on their chances, especially when you can just add a new Ganondorf to kill two birds with one stone.
I feel like it is just a possibility that people should at least keep in mind. There are a couple things like that such as Pauline being our Mario rep or Dixie Kong as an echo fighter that people should at least have this understanding that it is a realistic outcome, despite what people want. Would people prefer Captain Toad or Waluigi as our two Mario reps? Maybe, but I think people should at least prepare themselves mentally for Pauline being there. Would Dixie fans be happier if she was a unique character? Sure, but there also is a real possibility that we could get her as an echo fighter. Similarly, I could see us getting just a new Ganondorf as our Zelda newcomer, even if that means keeping Falcondorf and us not getting another Zelda newcomer.