I've thought about the same problem. I don't like the coins going back into mining rewards however, and I also don't like penalizing people who are ultra-security conscious and store their wallets offline with the need to log in once a period and shuffle their coins around.

However, the idea of a default future transaction is a good one, as follows: Imagine I can sign a 'transaction' that says essentially that another wallet can spend my coins after a certain date. Now, I can 'opt-in' to a system where I sign my coins to a 'back-up' service effective one year from now if I haven't spent them. Per our contractual agreement, if I lose my keys for whatever reason, they will sign my coins over to a new wallet once the time limit expires and they have access. This allows me to never give them access to my coins as long as I have my key, because before the period is over, I can send my coins to a new wallet and make a future-transaction from that wallet.

Obviously the period would be customizable, and there's trust being placed in the backup service, but its a way of distributing loss-risk around, and if you only 'banked' with local people, I'm sure local contract law would give you good recourse in case of theft.

-s