The problem I have with a multi-seat system is:
a) having to figure out how to do that
b) Gnome-Shell difficulties or general desktop panel clutter and multiple input (often I want a keyboard for the second monitor)
c) Most of the time I don't play games on Linux. I play CS:GO and Skyrim on my Windows boot, but I can't play those on Linux anyways So I'm more inclined to just keep things setup in a standard, easy-to-use way, and pass on the games that do work properly on Linux (Xonotic, Alien Areana, etc). I'm really hoping that Steam will properly support Linux games multi-head setups.
d) I've gotten those games to run, but there's always some difficulties. There must be a way to make a full-screen application function properly in Linux with a dual-head setup, and so I don't think I should need to change anything on my end, i'll just report issues and hope they get around to supporting my system better.
Thanks for the suggestions, though :) I am looking into any alternative options.
Also, keep in mind that some desktops such as Gnome Shell do not work properly with Zaphod Mode. LXDE and Openbox work, but only on one screen. KDE is supposed to work, I know Xfce does, and I have used Blackbox and Zaphod as well.
In Windows, there's no way to do multiseat for free. In linux you can follow this guide (which just happens to be Arch based). As another alternative that I personally find easier, you could look into xinput2 commands to spawn additional master input devices (part of MPX) and use your 2nd mouse and keyboard inputs in a xephyr window. It won't be GPU accelerated (unless you use virtualgl) but I've found it to be pretty effective alternative. I unfortunately lost a lot of documentation that I used to set up something like this but the xinput commands to spawn additional masters is pretty easy and seems to be exactly what you're looking for when it comes to multiple keybords.
I must be a rare case in that I have no want or need to drag apps from one screen to another, I run "separate X screens". I kinda just designate different screens for different types of task and run 8 virtual desktops on each. Everything works perfectly for me, full screen gaming included.
I can also confirm this behavior. Had exactly the same problems with multi-monitor setups on Linux for the past 6 years while gaming as described in the article.
Most of the problems could be solved, but only with some hack load of work.