I'm *very* new to the X Universe, but have been playing MS Flight Simulator since it's inception...we're talking *thousands* of hours.
I have four 27" monitors on my desk (3 across, one on top in the middle) specifically to fly Flight Simulator. (Running Windows 10)
MSFS has giving the choice for a long, long time to run full-screen or windowed. In full-screen, you get one screen, on one monitor. Period. In Windowed mode, I can "undock" any window or panel I choose and drag it to any physical monitor I want. Hence the 4 monitors! Overhead panel on the top physical monitor, gauges / throttle / GPS / etc on the right physical monitor, cockpit on the main (bottom middle) monitor, and email, chrome, etc. on the left monitor.
I miss that in X3TC/AP/LU. Running in borderless mode let's me alt+tab to use my cursor in other apps (like chrome, where I always have a universe map in its own tab, along with about 90 other X3 related tabs to figure out what the heck I'm supposed to be doing!
), but of course I can't drag any X3 panels / views to a different physical monitor, where I could keep info handy and "immerse" myself in my main cockpit monitor.
Just my 2 cent's worth, but X4 with multi-monitor display support would rock...and get my money!