But also, 100% compatibility would be odd, wouldn’t you just switch platforms if you wanted the different functionality.

I don’t think there’s much point to a fediverse if there isn’t decent compatibility between platforms, especially if they both comprise plain text posts and replies.

Beyond that, I agree, I don’t think these issues are hard. In more detail, a central issue is the simplicity with which microblogs format their feeds: everything is a post which are all assembled in a flat feed, with threading replies together being somewhat optional. There isn’t a sense of structure as lemmy/kbin have, with communities > posts > comments > replies. To me this is brutalist and unnecessary and limits the ability with which other platforms can be integrated. As mastodon completely dominated the fediverse, these limitations are actually somewhat severe, as a large part of the fediverse is constrained by this often without even knowing that there are other options.