Would this work better, if the "train" were so long that it would always be in contact with at least 2 rings? Also assuming that the rings are passive and the active components would be entirely on the train itself, similar to the Chūō Shinkansen. Either way, this is even more unrealistic than building a tube in the sky as a continuous guideway aka Hyperloop
Edit: typo
At the current moment, for practical applications, I agree. But at what point does an idea become worth investigating? Maybe a Sci-Fi screenwriter wants to have a futuristic but theoretically possible transport system between colonies on a moon with low gravity or sth