NIP-53 Live Activities has officially been merged.

I only know of two clients supporting live streaming activities. Amethyst and Snort (though direct client integration was removed from Snort after user's complained - OMG A CHANGE!).

You can start your own stream at https://zap.stream

https://github.com/nostr-protocol/nips/commit/141197c564d97073f0293e3b2f367f0b6b3619c2