isn't activitypub stuff basically open?
so you could create or comission your own platform/ interface that can synthesize posts from all sorts of places and could even do things about duplicates?
thats the benefir of the open source data model and apis - someone can probabledevlop the features you want - eventually.
the current platforms probably all look a bit like pre existing forums / aggregators or social media . butthats just a starting pont, the future could be much weirder ways of compiling displaying and creating posts. and in theory it can all interoprate (within reason, and outwith federation blocks)
i probably have no idea what i'm talking about though . . . i've certainly not even queried a single activitypub api personally