That’s an idea too. But personally I think this worrying about the dominance of a single site is a bit misplaced, assuming that the server uses the same software and protocols. There’s advantages in having some centralization. More resources can be put into the chosen instance to improve its reliability and its moderation. These need to be absolute priorities when trying to attract new users.

A certain encyclopedia site has a de-facto monopoly of the encyclopedia space. That’s not a problem because it has the right governance and ownership structure. I think the discussion space could perhaps use a similar site.