I also read an opinion piece that there should be a way to apply for additional state-paid holiday-days if you spend more than X hours on a train while going on holiday which I think would also be a nice incentive use trains as long travel-time is a big problem as well

going Berlin to Paris on a plane is not necessary much faster than going by train because of the time you spend in the airports so for those distances just regulating the price as a first option is good

for longer distances it would also be good if people would start using trains eventually (we seriously need far more night-trains)