I don’t think that’s the case, but maybe you meant something more specific than what you wrote? Several implementations support content-related AS2 content types (both base types and extensions) that do not fallback to as:Note or as:Question. For example, Funkwhale has “Libraries”, “Tracks”, “Audio” (etc.), PeerTube has “PlayLists” and “Video”, PixelFed has “Story”, Mobilizon has “Event”, and so on.
Unfortunately (in my opinion), that’s only hard-coded in the UIs. I often see “Note” content, from non-Mastodon servers or patched Mastodon instances, that are 1000s of characters long in my feed and the viewing UX is not very good.