Considering the large and affluent Vietnamese population in greater Los Angeles, LAX is a sure bet.

VN could do it with their existing 777's, if they stopped somewhere en route, such as KIX, couldn't they? A coordinated arrival time at KIX for flights from HAN and SGN could feed into a single TPAC to LAX. That might be better than, say, a single SGN-LAX ultra-long-haul or a SGN-HAN-LAX direct flight.