There are wonderfully simple programs such as "Music Star" that will permit even a five-year-old to create a midi. There is no need for a "Roland" (although one could be used) the individual simply sets the time signiture, and mouse clicks on a keyboard on the screen, save the file and make corrections.

It should be relatively simple to setup such an area "on a website" that would permit the easy composition of tunes by even the "musically challenged."

Then again, perhaps no one but the "musically challenged" would like to contribute in such a fashion, and the contributions may be more bother than help.