It’s quite impressive that the Sansa devs can squeeze in ogg support (though imperfectly, with the tagging problem), and also upcoming FLAC support.
I know others have requested file folder browsing and AAC support.
I’d just like to throw in my 2 cents and hope the devs can do gapless mp3. I listen to a lot of concert CDs and the gap between songs is annoying. Foobar can read the lame mp3 tags for gapless, and rockbox of course has the code to enable gapless, so I’m sure it can be done, and is probably a lot easier to implement than adding a whole new codec or two to support, though I am no expert on that.
Also, it would be nice to be able to know “time remaining” for when I listen to audio books. The original Sandisk Digital Audio Player (circa 2005 which I still have) does “time remaining” just fine. Even if it displayed time elapsed / total time, that would be better than the current situation of just time elapsed. I.E. 1:24 / 5:00.
That said, I think the devs are doing a great job. You guys and gals deserve a raise!