Two things I'd like to see:
1. Being able to use Spotlight in JRemote.
2. Being able to see lyrics in JRemote.
For both, I'd like to be able to swipe right, or press a button, to access these things directly rather than navigating a series of long-presses or nested drop-down menus. A button for each when in the Playing Now screen of JRemote would make, for me at least, a more enjoyable user experience. Particularly for lyrics which are a tag (I believe) and shouldn't need to be viewed as a pdf (which I don't believe the android version of JRemote can do anyway.)
My two cents: I use JRiver for music only. At this point, I'd be hard-pressed to name audio features I'd like to see added. The program does everything I want it to do though I'll stipulate that there may be things it could do but doesn't that I would want as well. At any rate, I'd like to see more advancement on the app aspects of the program. In other words, a more robust JRemote that more closely mirrors that act of listening to music with the band's booklet or album cover in your hands.