So one could create and send an unfunded coin..... the purchaser can transfer funds with the external public key - they can not withdraw funds without the sealed private key, and a subsequent holder of the coin can confirms the BTC balance with the public key, and accesses the BTC with the private key if they want to break the seal....

Works structurally - but is there some accomplice theory here that might be brought to bear on this?  Is there some way you cold be held accountable as a facilitator even though you have no participation, or even knowledge, of whether or not the coin was funded?