The relevant EU regulation says the trough-tickets should be offered. That's of course useless for the passenger as long as there are no sanctions if they are not offered.
The EU has only existed for 29 years - which is actually very little time for projects of this scale?
It's on the agenda for the next parliamentary session: https://jonworth.eu/tzitzikostas-at-his-ep-hearing-4th-novem...
Of course, it's technically possible, and not really all that hard. But is it politically possible? I doubt it. The EU doesn't even look like it's going to hold together long-term. If the various quarreling nations of the EU couldn't come together after all these decades and make a continent-wide railway system by now, I don't think they're ever going to.