I like this idea a lot. On an abstract level, I don’t think there’s any reason why a single post must only contain one “kind”. If I check in at a location and say I had a nice meal and am also enjoying listening to some live music, provided those are all marked up correctly with mf2, they could all go in the same post, right?
I anticipate some difficulty, though, with WordPress, because that would be a significant change for the plugin. Right now, post kinds are their own taxonomy, which allows a quick filtered view by kind (https://mrkapowski.com/kind/reply, for example). If post kinds become blocks in the block editor, we’ll have to rethink the whole architecture.