To conclude this discussion, when someone tells me "sure you could.... but good luck with ..." that basically means: "yes, you could use that, but it still stinks as a solution". That's not just my interpretation, that's a quite common way of saying something stinks.
Perhaps we're dealing with small cultural differences here, because this is simply not true where I live.. the "good luck" construction is just a sarcastic way of presenting a downside which, if not applicable in the current situation (e.g. Jon knows this shop that always has nice suits left, or sazeMaster does not need the script to work anywhere else), does not
invalidate the proposal as a whole.