[quote=@Tlstiffl]
[@BrokenPromise] I definitely agree with everything you said, which I think is why no one does it. 

Your idea of using an old RP as a world builder is pretty cool!
[/quote]

I know it's late, but I asked people for the right to use their RP Setting before; my most successful RP ever involved a setting I borrowed from a friend (who allowed me to borrow it) that I then redid most of the lore for, then retooled from an Academy RP to a War RP (although the location used for the Academy RP version is still canon).

So if you have permission, it's fine.