I can't imagine there won't be major improvements to conventional high speed rail that will be able to run on existing lines. This requires an entirely new track that can't be used for anything else and the trainset itself can't be upgraded as easily as it is tied to the track. These will be also limited by the noise they produce; even if they can go faster in theory noise pollution is going to be a major issue as is. I'm not sure they have solved most of the tunnel boom problem; a major requirement in Japan.

So I wouldn't expect there will be a lot of room for improvement of this design over the next 30-60 years. It will probably cost a lot more than expected as well. Comparatively, there are a lot of new technologies that could deliver major improvements in transportation efficiency and speed without the large capital investment of a maglev line over the next 30-60 years from traditional rail to self-driving cars to new aircraft.

I'm really skeptical of the wisdom of this project to be honest. If you want a maglev design you might as well go with a near-vacuum tunnel and more than triple your speed rather than just increase it by 50%. This would also have the advantage of eliminating the noise issue. I believe China is looking at something like that.