Mute Thread
Dynamic loading of subthreads so huge threads can be loaded efficiently
Scheduled Notes
Date Range on search / feeds
Push notifications on mobile/desktop
A bunch of other small things, too (and a few really big ones like group chat)
Discussion
Personally I think mute threads and group chat could be more useful than badges but there's always the cutting edge aspect that motivates.
Relatedly at times I wish the chat entry box at top of screen could be in a div that I could drag/drop to rearrange somewhere else on page, and be able to work on a post while switching filtered views.
You've done such an awesome job on all this.