If you send a transaction with no miners fee, and miners are only accepting transactions with a certain amount of fees (im assuming the blocks are full at this point) could you then go back and add a fee so that the transaction doesnt remain in limbo forever?
I've got a bounty open for a solution to this problem with replace-by-fee, allowing you to change fees after the fact. But it will be delayed for at least another month at the request of a few sites who could be harmed by double-spending enabled by replace by fee.
It will come though in the long run.
