Power consumption seems a bit high. Other than that, looks awesome.
I checked, the 2nd gen iPod mini can get 18 hours of listening on a 400mAh battery, with a spinning HDD. This is getting 20+ hours listening with a 2200mAh battery and solid state storage.
Not that 20+ hours of listening is bad, I just expect a player with a battery that large to do quite a bit more.
You may need to build it yourself, but it looks like everything a HN-using MP3-buyer would want.