When MGS3D comes out if MGS3 is not available on the NGP by then (since it seems safe to assume that the NGP will get PS2 titles on it, I'd think).
Probably after I get a NGP though. It's not high on my list of things I want right now, especially since just getting the system alone would put a dent into my cash, plus paying $40 per game doesn't help. Not really criticizing the prices, just my finance isn't exactly "large" at the moment.
EDIT: And yeah, I'd take the PS2 version of MGS3 over the 3DS version, mainly because of controls. I'd rather have the dual analog stick control than the better graphics and 3D (unless they completely remake the game and give it the new third person shooter perspective of Peace Walker).