I'm doing two things I don't like to do but I'm not sure that I have the skill or creativity to get around it so here it is. The only thing that would make Subsonic be better for me than any other player I've touched is the addition of some sort of automatic playlist creation function (I know about the Random Playlist function).
I know that there are different ways to suggest music and I think iTunes Genius might be the most user easy way which may make it the best to emulate. I'm not sure exactly how Genius works but my guess is that is uses sales data (if you hit Genius on some Katy Perry song, it looks up other users who purchased that song and creates a list of the most purchased songs by those users). As Subsonic doesn't have access to sales data like Apple does, I'm not sure what a good solution would be. I doubt Subsonic users would want to be sharing their song play data but that might work. Another option, and I have no idea how legal this is, is to use an iTunes Genius file in the same way that iTunes does as it's saved locally. Similarly, there are other services that use "music fingerprints" to suggest songs (see MusicDNS). Otherwise, I have no idea how to make that work.
So things I hate doing:
#1 - Suggesting something that I have no idea how to do and can't offer much help to bring to fruiting.
#2 - Suggesting something that is similar to something a competitor offers.
To try and offset #1, I'll be donating some dough but don't expect it to result in me getting what I want; not because I don't think it can be developed but because I don't assume that I can throw money at people to get them to do something. To try and offset #2, I offer my ability to write algorithms and I'll try to be as creative as I can but I'm not sure that I can do anything that can't be done by any developer.
Anyway, there's my suggestion. I'll help in any way I can.