Alrighty well anyway it occurs to me that this idea is pretty much exactly like a coin mixer that gives out a physical receipt in between accepting coins and giving back out the anonymous coins. The physical receipt can be used as cash indefinitely in the meantime which is worth some amount of anonymized coins at the mixer later. The mixer needs a way to identify counterfeits, which i guess can be done if the receipts are smartchips.

The problems are:
How to make the mixer trustless as far as redeeming coin
How to make the mixer trustless as far as minting a receipt that it can't duplicate