It’s not a choice between 1 car-train or 1 normal night train - you can have both if there is line capacity.
And you probably aren’t running sleeper carriages during peak hours.
cry-laughs in German Oh hell yes we do run at nominal capacity, actually often enough above. The transit routes are fully booked all times of the year, the demand for freight transit is insane, and every bordering country is complaining that we can't get our shit together (to no one's surprise after 30 years of perpetual budget cuts).
The problem is: virtually all trans-European routes run through Germany. You can't avoid running through here.
>> You also need special facilities and longer stops, because cars can't just dismount at normal platforms in a couple of minutes.
So what? Point-to-point with no stops in between. Works for the chunnel, too.
The future of personal transport is not IMO private personal cars, but this will help the transition