MP3 is a pretty smart piece of sound engineering, dropping sounds that most of us can't perceive, but it would be foolish to think there can't be better.
If I had something on a lossless file on my desktop machine, and something came along that would measure my hearing and compress in a way that took my personal limits into account, the result might be better for my ears, and compress better than MP3.
Fanciful? Well, the big problem is the measurement of the response of my ears, but they only get up to about 12kHz these days, and compression suited to J. Random Teenager could include a lot I cannot hear, so maybe a personal compression standard would work.
But if there's something like that, we're going to need a lossless source for the compression.