Split monitor into virtual monitors in Linux

Question

First my problem, today I have two 1280x1024 / 5:4 displays, I'am planning to replace them with a widescreen monitor, aiming at 2560x1080 at this moment.

I'm running MATE desktop environment, all is fine, my system detects two monitors, I have the panel on one where I have my apps and menus and windows, the other one I can put windows on it and snap windows to that screen.

MATE is very limiting, it's not a tiling window manager like xmonad for example, I don't want to change from MATE either and want no answer regarding this.

If I change to such a monitor, the panel will stretch over all 2560 pixels, and the snapping will stop working in my version of MATE, the snapping can be solved by upgrading MATE, but the panel would still be stretched as there is no explicit width/height option for the panel, only size which is the size from which side the panel is orientated. I also want to fullscreen apps, videos and games so that it will only stick to one display without interfering anything on the other.

There is an non-Linux version of this question here: Split monitor into virtual monitors

There are also multiple Linux "solutions" with xephyr / xrandr / vnc, which makes a window to a virtual monitor and makes it a hassle to make a seamless solution between the them

Some monitors also have picture-by-picture (PbP) / dual link-up solutions built into their monitors which can use multiple input sources. But none seems 100% perfect and there are really not many videos or images on how the system really works, most reviews just mentions them fast but never shows them or their potential, some Dell variants can't handle filling all the pixels, and the developers doesn't even think this is a problem.. leaving BIG gaps on top of bottom, LG's implementation seems like the best one after reading a lot, signaling the right resolution back to the system. But again I would imaging there is a big problem changing between a PbP setup from one computer to another with fullscreen. Not simply changing between those with one press.

As a long Linux fan I believe there must be a better, more seamless, software solution to this problem with only one cable, bring it

xephyr could maybe do the job, I'm not sure but I haven't found one yet, xpra or xdmx anyone?