Aren’t you describing Mastodon/StatusNet etc? I can’t recall if they have channels, but they might already.
Way back when it was Identi.ca I joined that, and was reasonably impressed, but very few “big names” joined the network. I seem to recall Stephen Fry on there, but that’s really it outside the niche world of tech.
So if we wanted to go that route, we’d somehow have to get the “big draws” onto the platform early on, and there’s no incentive for them to do so.