Restricting it might be useful as to not dilute his idea and make it unappealing to die-hard 'indie fashionistas'. Perhaps making his code generic, were this to ever be completed, would be useful in creating spin-offs.
the idea itself is reusable. suggestion engines could always use improvements.
if i could come up with a truly good idea offhand, though, i might be working on it instead of sharing ;)
i'm sure there are other relevant applications for this concept beyond the big ones.