this is a tricky problem. generating a new key and sweeping the funds to it incurs miner fees. opendime has created an interesting solution. the USB wallet device is disposable and must be physically broken in order to spend any funds kept on it.
as long as the device is intact, you can check the balance and use it for trading.
Shit that sounds so crazy it just might work
My current line of thinking is that yes we need a type of "Money network" that will work like a type of recorded post system
but it does not know anything about whats inside the letter, only that something was sent digitally and received in case of disputes
and also deals with routeing.
That's the easy part and is KISS and you seem like an educated person and will have to work with me if you would like to know more
but it does include, as much as i would like not too, trusted 3rd parties that are anomalous entitles that get voted out the system if
they cannot behave themselves, much like what happens already today on networks.
Will peg the post and check for reply tomorrow