I think it needs to be said, in Christopher Lambert's voice:
"There can be only one."
But to be serious: I think the gaming community can support several. Back in the day, there was TSR, Judges Guild, and Mayfair Games a little later. I think all three of them would have flourished more if not for eventual lawsuits. And there were many, many other games like Arduin, that were known a bit less.
In 2024? I think there's room for a number of moderately popular D&D alternatives. Especially if they can make them compatible with the new Edition's rules where you can just bolt on a new class or rules system.
But, and this is a big but, VTTs make things more difficult. It will be tough to put all of the different rules together with D&D for online gaming. And since that's what I'm pretty much going to be doing, that makes it more difficult to figure out in the end. I think if you have a VTT that can easily put different rules together, that would be something special.