There are many parts of China where T trains are still top of the line. Or even K trains! I think it will be this way for a long time to come.

Even in relatively wealthy East/coastal China, I think there are a lot of Chinese who could...but would rather not...spend up to the D/G fare. For a personal trip, I'd rather spend RMB 320 for overnight hard sleeper in T than RMB 700 for a day seat in G or sleeper in D. (Business trip might be different choice.) And right now, the reliability factor of the old-style trains is more comforting than the Time Schedule Roulette on the HSR network. Of note, the D trains were running fine and on schedule on the BJ-SH route, until they started up the G service. Now anything on that track is subject to getting boogered up.