Seems like a good idea. As the weight ratio train : passengers decreases, I guess the experience is zippy when empty, slower when full, wonder if they adapt the schedule accordingly ?
As for reducing the lifetime embedded emissions - how does the construction of the trains compare to the construction of the tracks - I’d imagine the latter dominates - can they replace concrete and steel elevated structures too ?

And naturally in the comments come the sinophobic “instant experts” who make up all kinds of idiocy to cast shade on the achievement.