I think it would work fine. The new Nationalities, (Chicoms, RoKs), a few weapons changes, some different unit designations... I'd prefer more maps (always cool to have more maps), but why not? That would be cool - count me in if they do that!
Actually I've been thinking for some time that that would be the natural "end" of the CC/Pacific engine, once you assume (but "never 'assume' anything in CC!") that the game system will be thoroughly exploited before Chad & his people will tire of it. I have the strongest belief that a CC:Vietnam would be a really, really great hit, and also a good commercial success.
CC's the monkey on our back, Chad the cruel pusher.