This is how it is today, but imagine you need to do pre-boarding to trains by TSA one hour in advance, increased density for seating so that premium-economy can be sold at a higher margin, baggage limitations and payment per kilogram, restrictions to wear a belt at all times (no moving around allowed).
These restrictions were added to flying one by one, boiling the frog. It can and it may be implemented for trains also.
- More space (including the Chinese ones). While it might not be wider than a plane, it's order of magnitudes longer. So, each row has less seats, and rows are much farther from each other than on a plane.
- More room for bags and suitcases as well. There's usually no need to check your luggage, unless you have an excessive amount of them.
- No turbulence
- You can stand, walk, eat, drink, open the table, work with electronics, etc. at any time.
- No long-ass waiting time before and after. For a 8:00 train, all you need is to be able to walk onto it at 7:59. Whereas for a plane, they won't let you on unless you are present at the gate before 7:45 (the exact time depends on the airport). And not to mention the security checks.
- Quietness
- Air is better