I've thought of exactly this same thing. It would need to be implimented as a fork of bitcoin, and would need a new transaction type. If no transactions are ma

I've thought of exactly this same thing. It would need to be implimented as a fork of bitcoin, and would need a new transaction type. If no transactions are made from the target account after say 5 years, then the balance would transfer from the target to the initiator. I couldn't figure out how to prevent miners from just targeting bunches of inactive accounts though... of course it's the miners you want to get on board, so maybe it's a good thing? You'd have to balance paying miners an immediate commission for including this transaction against the 5 year wait and gamble they would otherwise have.