I personally would love to see a fediverse alternative to something like StumbleUpon, which I always found to be quite unique in the realm of social media.

I also think having something like Spotify with social features powered by the fedi would be neat (I realise technically funkwhale is vaguely this, but in execution it really isn’t. It’s federation is pretty basic/not social). Thinking something where you can easily start listening parties, share music to friends to listen to, find song recommendations from friends likes, etc.