I could honestly see the Democrat Party fracturing. It's not likely, but it's possible. However, I don't think that'd be planned and I think a lot of the moderates would come to the Republicans.
If you look at Biden's numbers, there's a floor there. These are the 'vote blue no matter who' folks. The Republicans have similar people. Their attitude is basically "I don't give a shit what's going on, I'm a Republican/Democrat and that's how I'm voting".
I was a kid, but the first election I ever paid attention to was H.W. Bush, Clinton and Ross Perot. Perot polled reasonably well and then didn't (I can't remember why, I was 12), but he didn't have that floor. There wasn't that contingent of people that would go out and vote for him no matter what.
There's a certain tribal identity that comes with two major parties and it guarantees them a certain level of support. That takes time to build and leaving those parties behind means you lose that, and when you lose that, you lose your relevance.
Just my take.