Honestly, nothing comes to mind. We got mini posts, blog posts, lists, streams, payments and even market places (it is in the spec, but I haven't seen a good implementation yet) and even DVMs. Now, what I want to see the most, is for those things to mature into proper, big apps, to build an ecosystem around Nostr. In the CPU development, people often use the "tick-tock" idea; a tick is a substantial increase and a tock just an iterative one. I think that Nostr should "tock". Improve on what we have and increase reliability and spec compliance. We can tick once a bit of stability has been here - meaning that a new base to be shaken by the next new cool thing would be ready. :)
Discussion
I totally get this.
Most of nostr's apps that we see as "all these cool things coming together" are very much in an experimentation stage - We all hunger for something more mature, to be daily-driven by the average user, which we can sell to anyone else, and especially given its nostr, to have tighter integration within itself.
A likely stupid but worth-considering example - What stops me from being on 0xchat and receiving a notification that a user I follow is about to stream on zap.stream - We can argue all we want about whether we'd want this, but I think it's the potential for integration that nostr has - One eco-system, one protocol, a myriad of inter-connected experiences.
I think we can all see the end-game, and it's just about within reach - Except it's not.