Not a "free speech" Twitter, not a "better" Twitter, just... figuratively rebranded Twitter. Same concept, maybe different implementation details, some modest innovations, but give the people who want to leave a place to go.
The only answer I've ever gotten (that isn't solvable by being good at software engineering) is, "network effects!" but... now is the moment, if ever there was a moment, where the network is most fragile on Twitter.
Give people a place to go for a "Twitter Classic" experience, before the rudeness and hate get re-platformed!
Whoever does this, I feel confident in saying, will be a millionaire. I dunno if there are any more "Social Media" billionaires left, but millionaire? That feels very achievable!