The question is whether there is a guaranteed exchange between the in game currency and the external cryptocurrency. If there isn't, it might be hard to convince people to still deposit real, externally usable cryptocurrencies. If there is, the in game currency might be regarded as a unit of account for the external cryptocurrency, and thereby possibly a collision with the EULA.
I haven't read the EULA in a long time, but I would assume that depositing for virtual currency within the game would break it already? Since, most games don't allow the sale of in game currencies, and I believe Minecraft also didn't allow purchasing of any non cosmetic items, which a virtual in game currency would violate that.