The amount of tokens/coins you would have to get would have to be pretty big, because all the while you are gaining currency to get the exact gear you want, there's also a chance the gear you want could drop at any run. 3-4 coins per item is a pitiful amount. You'd get your item so quickly. You are working with the assumption that if people have better means of getting the drops they need, they'd run the alliance raid more. Well maybe for a few weeks or a month, possibly two, but afterwards we are right back where we started and perhaps even worse off since people who would generally be grinding the raids for a long time are gone as well.

I'd say if we were to work with this kind of token/coin exchange thing, they would have to be something you roll for from the alliance raid chests which are guaranteed to drop and you can only win one per raid, if you're lucky. That way you always have a chance of slowly building up to the item you want, if you are unlucky with the drops.