The thing that I'm really interested in seeing and is actually more of a meta-layer is new kinds of notifications - this may sound incredibly boring haha - but if you think about the kinds of notifications that 2009 / 10 facebook and their developer platform offered - I think there will be a resurgence in these kinds of experiences built on nostr. I think games is an area that could massively benefit from this - but also any other consumer social products too. Even the simplest notification you might want to build:

"9 of your friends joined {app} this week!" is impossible with the current locked down social platforms / contact list permissions.