songsmyth wrote: when I want to share 1 monitor between multiple pis. I wan't to be able to see the gui from each pi, when I want, so "just ssh" isn't a viable solution for me!
I don't have this perfect, but I am going to suggest including ssh in what you are doing but with the -X option. What I have is a central system that is running X2Go. I can view this system from various machines. From the X2Go system, I can then use ssh -X to any pi or other system running Linux, even one that isn't running the desktop itself locally but has enough files to support X. These systems can then run individual X programs such as firefox.
I also use byobu mostly from one central machine to control multiple ssh logins that aren't using X on various machines. So when I switch from one machine to another, all I have to do is run a script that I have in the path called 'reattach' and all those shells are switched over to the new location.
In the past, I've had this sort of thing set up with multiple screens, sometimes with dual heads and sometimes with dual machines each with a single head, but the way I've configured the main machine right now makes that something I need to work on. But in principle, one should be able to have any number of monitors at each station switchable with just a script file.
Ideas in that direction include having two monitors each of which is running a different remote X2Go but share keyboard and monitor. This could be a pi connected to each monitor which has the job of viewing and displaying one screen from the main machine. The screen sharing could be done with Synergy, https://github.com/symless/synergy