Kbin has a separate tab within a community called “microblog” I think. Any hashtags set by the community are automatically followed in the “microblog” feed and can be fully interacted with.
This doesn’t bring threadiverse content into mastodon, but it does bring kbin users at least, into mastodon.
And with the @ing of lemmy communities, you can post from mastodon to lemmy. There’s some work to be done, for sure, but I think we’re close to a decent solution.
But also, 100% compatibility would be odd, wouldn’t you just switch platforms if you wanted the different functionality.