IMO they’ve got a better shot at getting it built with this attempt, particularly because China has an economic incentive to assist, and has been slowly running HSR through indochina for a decade now, but have had blocked by lib parties who don’t believe in spending on non-car infrastructure, but I’d be more optimistic if they were already laying rail for the Kunming-Lao Cai or Nanning-Dong Dang legs. It’s harder to stop a project when the smallest portions are already showing economic and social benefits.
China also need to find work for its diminished construction companies, which are still a giant part of China’s economy. So I expect rail equipment constructed in China to be cheaper than normal and the engineering teams to have a lot of experience which will make design quick and cheap.
That said, I agree that Vietnam should engage in staged construction of the railway as Vietnam doesn’t have the bankroll that China had when building out its system.