Man I just typed out a huge response as to why this doesn't make any sense and in so doing realized why it makes sense. That is brilliant. Yes it makes perfect sense. Though you dont need a 24 hour limitation. You only need to time limit it to as many blocks as we expect a merchant to need in order to feel secure. 6 maybe 10. 24 hour time lock would allow you to do thinks like buy your own private island with an instantly secure transaction but there is a tradeoff there. is it really worth locking people out of spending their funds for a full 24 hours just so a couple of guys who do HUGE transactions can feel instantly secure. Or is the better trade off to not let people make instantly secure HUGE transactions but also not have to have their nxt locked away for so long.
*edit* note that its still vulnerable against an attempted quintuple spend attack .
I agree, its a great idea to hold NXT for instant transactions, I just put a response in the linked thread to see why it can't be done using a reserve balance on the normal account otherwise we have further complexity for the user.
also note that transparent forging would have to be proven first before this could be proven to be 100% secure.
I do not think both relate to much to each other. Instant transactions rely on the network distributing unconfirmed transactions faster than the merchant selling.
There is still no such thing as TF. The current implementation of consensus finding is susceptible to 33% attacks.