You know what's interesting? A Decentralised media platform used to be huge and actually is still huge: Torrents. There's a huge community that consumes media that's not hosted anywhere particular and there are apps like Popcorn Time that offer viewing experience almost as good as Netflix. The problem, of course, is that up until now there was no way to reward the creators and almost all the media consumed on Torrent…
Perhaps the biggest problem with Youtube is discoverability. Youtube's algorithms determine what you will see next. How is that solved on the decentralized platforms? How does discoverability work, what assumptions does it make, and can it be "gamed"?
The technical aspect of this is a mostly solved problem (YouTube and other distributors do it) but getting past the privacy aspects will be challenging - the type of person to use a distributed platform will also likely be using it to avoid this sort of tracking. Or they're in a country that has GDPR-like laws.