Apropos to the discussion above of UO, just did a short round trip with them to Hanoi. The flight was codeshared with CX which I assume allowed for connections and possibly lounge access, and the planes were full each way.

I bet they could add another service on this route and do well; the early morning flight times clearly didn't deter people but more might want to fly it still with other options.

They could also probably afford not to pad the schedule so much and motivate even more traffic; advertised as 2h but closer to 1.5, it's a route that's not really much longer than Taiwan.