Doing that would require decoding the original music file, mix it with the next track (taking into account different bit rates etc), and finally re-encode it. This is somewhat against my philosophy of keeping things as simple as possible, but I'll keep your request in mind.
Another thing that I find useful is sorting Soong by Gener. Let's say I want slow music, evergrin, chill or dance. A wold like to clik on button and search for that kind of songs.
Again Thanks and hope that this project will be project of the month.