Parece que o Projeto X Multihead Distribuído (DMX) está fazendo isso:
Current Open Source multihead solutions are limited to a single physical machine. A single X server controls multiple display devices, which can be arranged as independent heads or unified into a single desktop. These solutions are limited to the number of physical devices that can co-exist in a single machine (e.g., due to the number of AGP/PCI slots available for graphics cards). Thus, large tiled displays are not currently possible. This limitation will be solved by eliminating the requirement that the display devices reside in the same physical machine. This will be accomplished by developing a front-end proxy X server that will control multiple back-end X servers that make up the large display. These X servers can either run on the same or separate machines.
Mas, de acordo com a página de download :
The DMX software has been integrated into the X.org server software. Please download directly from X.org instead of from SourceForge. The code here is rather old and is no longer updated.