I find my experience here has been mostly solid, so I think you mostly have your priorities right. It's also fun to see experimentation with new features every now and then, so I'm not sure I would even like to see a shift towards focusing only on important stuff.
Better handling of video content #147 (I am also interested if PieFed can integrate better with PeerTube, for example an option to browse PeerTube channels)
"Announce does not federate properly with Lemmy" #22
I think there's a lot of potential in better integration with services outside of the Threadiverse, and this is something Lemmy has been notoriously bad at (and its developers seemingly uninterested in). Not that PieFed should become like Kbin and serve two separate functions, but there's a lot to be achieved in both ends by making the services more interoperable. There might be some sort of place for both boosts and hashtags, while leading @mentions might sometimes be justifiably hidden. More than important I guess I would find it fun.
As for what's urgent, ensuring core functionality and GDPR compliance seems like a fair priority.