The sponsor gift at the Animalia Romana EF (don't remember what number that was) was a coin. It's nice to have that, but something like that only works as sponsor gifts or maybe a limited run by one of the dealers. Trying to establish and force another currency into our financial ecosystem makes no sense whatsoever IMHO.
I mean, if someone wants to make a run of coins, and guarantees to buy back the coins at their assigned value, so each dealer can decide whether he wants to accept those for payment as well, that's fine I guess.
But neither enforcing their use, which would complicate the exchange of currencies for our non-
EMU-guests even further, nor generally Eurofurence paying for their fabrication in advance just to allow for their use as a payment alternative with uncertain acceptance rates, etc, is worth its expense and potential issues.
If
you personally want to be the above mentioned dealer that acts as a bank for these, I personally—not talking as a representative of EF here—see no reason why that should be prohibited or anything, and I'm sure if you ask nicely, Alpha_Ki might be willing to start a dialogue between the other dealers and you as well.
Oh and another thing: While the staff of several of the bigger furry conventions overlaps and a lot of the overall furry con staff are good acquaintances or even friends, no con will ever (be able to) force another to go along with something like this. You'd have to negotiate this with every single one of them. They're all run independently, there's no central authority.