I've been playing with Xdmx on 2x computers with 4x screens since I've got an interest in some stuff that would benefit from a lot of display space. I can report that Lazarus ran well with it provided that X's rendering was disabled, but unfortunately lots of other stuff- in particular Firefox/Iceweasel- was far less tolerant, either crashing or being glacially slow. There were also lingering keyboard layout problems.

A compromise appears to be x2x, which allows a single keyboard and mouse to control displays on multiple computers. However in this case windows can't span multiple displays, and can't be dragged between displays.

Noting that Lazarus runs well over SSH, and that this extends to apps written using the LCL, is there any way of specifying that a newly-created form should run on a particular (non-local) display, or of moving forms between displays?