Yeah, precisely why it's awesome, if you actually already have the glass already, then you don't need to invest in a new system (though, how would EF-S and crop glass work, I can't say). Being able to use something like a 50 f1.4 as a f1.0 lens with f1.4 DOF would be fucking pimp.
and yeah, it would make it easier/cheaper, if it wasn't already a 400$ investment haha.