Well I might just give it a try when I have some time on my hands, just for the heck of it. I really like the blossom and Nostr parts of your take on the watchparty idea.

However moderating the rooms, allow vote based skipping, leader assignment and it's edge cases like leader inactivity/disconnection etc. were the most annoying parts (also why I gave up)

Nostr login would take much of the user account storing it of my hands. Blossom would allow extra advertisement-less media source, which could be huge plusses