But it seems to have gone by the wayside as the upper limit is really the number of video outputs, and driving 30+ displays off one computer starts getting into custom setups that are going to be more expensive, even if the goal was just running 30 instances of Firefox on one computer. The wiki hasn't been updated in 6 years, so I assume it's not viable in modern Ubuntu?
Procedures are more or less same for every Unix or GNU/Linux systems. You somehow get dozens of display outputs, give Xorg with necessary config as to where to output and what input to watch, and run it. Unix and Linux are a multi-user operating systems so there's no inherent problem with it. Windows can do the same using the feature called Terminal Service. macOS Server had the same kind of feature years ago.
On GNU/Linux, DisplayLink(not to be confused with DisplayPort) USB graphics adapters should work for this, or virtual framebuffers using Xvfb can be used to connect over VNC or RDP. Or some sort of PCIe hub can be used to connect grapevine full of Quadros. Whatever.
The practicality problem of it is user experience tends to be rather suboptimal due to collectively massive issues, from network overheads, hardware acceleration issues or lack of support for it, workloads of sysadmin to constantly fighting outages, cost of client console hardware that aren't supposed to be full standalone computers but virtually it, etc.
It surprises me that it works so well, but I think that the original technology was designed exactly for this.
It sounds like the idea was to use it at the same time.
That's what we're talking about here.
https://en.wikipedia.org/wiki/Compatible_Time-Sharing_System