I'm not sure the stereotypical Vietnam mission would fit well. The game would have to stick to the more conventional, stand-up battles against massed forces to be much fun. So, okay, maybe it could be done- Ia Drang, the retaking of Hue, Hamburger Hill- these could make interesting play. If the campaigns could include non-U.S. forces such as the French and the ARVN, interesting battles such the near-destruction of Groupement Mobile No. 100 and the 1972 Easter invasion could find a place.
The problem is, of course, the emotional and political complexity. Too many people, particularly Americans, have strong feelings about that war. When they see ads on TV there would be shouting.
Here's an idea: how about a Korean War edition? Combat was relatively conventional and not too terribly different from WWII. Could be fun...