I’d probably post quite a bit of content (music, etc) on a youtube alternative if I could expect it to not be copyright-striked. (and if anyone would watch it. The current PeerTube instances seem very barren.)

3rd-party Twitter clients are going to have quite a spike in popularity then, just need to implement clientside blocking. It won’t prevent the person blocked from seeing your posts, but that’s kind of impossible to enforce on a public platform, anyway.