I'd like to modify this concept a bit in a universal way.
I'd like to lock a portion of my account (up to the whole account)
I want let's say invent a turtlecoin with value xx_NXT, grant a specific account (other or mine) the right to pull this turtlecoin if he sends a password and define a timeframe during this has to be done. after the timelimit the turtlecoin becomes NXT again.
During the timeframe the turtlecoin is locked for me.

this way the NXT-client could print a QR-Code with the generated password, I go to the petshop and the owner can pull the turtlecoin with it.
-> I get the turtle and both are happy  

this is of course only one application for this feature. of course turtlecoin can be replaced by amout xx NXT.

another idea: it wouldn't be hard to implement an escrow this way.

I wanna sell a turtle. buyer sends me pass for turtlecoin, which I only can pull after turtle reached buyer succesfully.
if he doesn't confirm turtle reached him alive, the turtlecoin becomes invalid for me and him also and goes as NXT to a predefined social fund.
the buyer can trick me, pretending the turtle was dead, but he won't do this very often, because the network stores unsuccesful trades.