@Gargron why would you want to give your privacy away for free when the 9 Euro ticket is much cheaper to manage (it’s all tax money anyway) and anonymous?
Also, can you imagine installing tourniquets and closing gates and accesses over Infratructure that was never meant to be closed on the first place? The first thing that will be ruined are th elevators for disabled people and prumps, as in Germany they are built to access directly the trains from the ground level.