A question i have is why would anyone want to use anything else but mp3s?
I see requests occasionally on this site over the years to add these formats to the player, however none of them have proven successful, and most are cumbersome and have a complete lack of support which makes them even more difficult to use.
This is not to say that MP3's cant or wont be replaced by a better format down the line, but based on the current storage options, support, and small footprint of decoding software and hardware, why would you go with anything else?