I think this could be a pretty popular thing if implemented correctly. I would probably use such a site instead of buying giftcards for amazon @ a 10% markup rate.
I considered the demand too low for such services (maybe wrongly) and the fact there are already a few websites (as quoted) old and established for some.
Basically, I could even process to pay the bills instantly for the EU and use other currencies for others. As well, a gift cards option, (with a 1:1 rate and no crazy rates). Can't say much, in case I was wrong (I'll do a KW research again) but it was something a little more advanced