We shouldn't actually do this because mastodon is not good software and will probably be obsolete soon, but if that were not the case.It would be a strategic win for EA to conspicuously fund the development of a community notes feature for Mastodon.
Here's what I think would happen: most mastodon communities would shit on it and refuse to use it because it had EA funding, but not vehemently enough to remove the feature from their forks, so this would just result in them looking incredibly wrong and bad and guilty every time anyone saw a successful community note.
And also: Community notes is the kind of feature that we should expect to actually substantially improve public policy discourse so it's the kind of thing we should be funding in earnest.
But I'm not sure we should work in that area. It's unfortunate that a global forum probably can't rise to prominence if it's received partisan funding, even if it's bi-partisan, as Argumentum ad Aurum is live and well and cavorting all around.