Going over the transaction specs, I noticed a "lock time" attribute on each transaction.  With this, there is apparently some sort of protocol envisioned for being able to push transactions to various nodes but also require them to be included at some future block instead of being processed immediately.  In other words, it is a request to miners to not include the transaction "no earlier than" some particular block number.  In addition, there is the ability for details about the transaction to be modified subsequent to its inclusion into a block.

My question is in a couple parts:  Is this in the roadmap for getting implemented in the future or is this simply an idea that hasn't really been completely thought through?  What kind of security issues are there in terms of a 3rd party "changing" the transaction information and simply updating to a new transaction version?  Or is this a "no later than" type of notification where the transaction expires after a certain block number has been created?

It is an interesting feature to Bitcoins if it could be pulled off.  Apparently most miners are not paying attention to this attribute as well, and it may be something to reconsider.