Reddit mentions of Osprey Ozone 28"/80L Wheeled Luggage

How big are we talking about? People routinely travel with suitcases that aren't a carry-on. Trains are used for long-term vacations. If you're imagining the interiour of a German train to be like an airplane, then no, it's quite a bit roomier.

It gets problematic when people are incapable of lifting their suitcase in/out themselves - there will be someone helping eventually, but it holds everyone up.

Also, the suitcase should fit in the luggage shelves (that take most of the common sizes), or the corners where people also places suitcases. Sometimes, people leave these huge suitcases standing in the corridor (presumably because they need to keep an eye on their precious), and they're told off by the conductor, as of course the corridor needs to be free.

I found you a photo. This is what people routinely travel with. Here is another one.

I'm using this for longer journeys now - 80 liter volume.