Install an old GPU, Connected a monitor to the extra GPU, connect mouse and keyboard, Use the loginctl command to list available devices/usb ports and attach them to a seat.

I suggest using Arch linux although loginctl should be available in all distributions using SystemD now.

If you don't have enough USB ports you can use a USB hub, some monitors comes with USB hub. And some with built in sound, or you can use wireless headset.

My main issue was that driver support was dropped for my oldest GPU card. So one day when I upgraded the OS it just stopped working. So to be on the safe side get another GPU like the one you already have.

Sorry being IT guy I wondered about the logic. I understand the need to align. But if one fail all fail and children like customers … not the patient kind? Or you have two system within each … then across the …. Sorry cannot stop my mind spinning.

The kids will get over it lol

[delayed]

So for a GPU with say 4 display ports, I can run 4 sessions off the same GPU provided I can get enough USB ports.

It might be possible one way or another, although I used separate gfx cards. You might find a different x server that lets you do it using a single card. I suggest getting an extra hard drive, install grub so you can dual boot, install the experimental OS on the extra hard drive and start fiddling. I also dual booted different OS in order to experiment with machine learning when the kids was sleeping, as I got multiple gpus, although the old ones where crap it was a good learning exercise.

Modern GPUs aren't constrained by the number of ports. You can use DisplayPort MST (hubs) to output multiple displays off a single port.

But most GPUs are limited to being able to run 4 displays. Except some AMD Eyefinity can do 6