too much coding and would strain a good graphics engine. Although graphics cards may be technologically advanced, they are still bottlenecked by the processor and motherboard. Having the possibilty of having to render twice as much information (say you are on one side of a map, your buddy on the other) I dont see hardware being able to keep up with drawing both of these(rendering long distances is usually helped by fogging). The graphics engine would have to be scaled down to accomodate this. when computers have the power to do so, the engine would still not be able to support as much as an engine that is only concerned with running one screen would be. its then not economically advantageous to have the engine because people (mainly "hardcore" gamers who make up the majority of the game buying population) would much prefer to be able to have the engine with all the bells and whistles that looks awesome, rather than having a scaled down engine with the novelty of having split screen. Coop (like Team Death Matches, etc) are commonplace now, and are quite easily set up overmultiplayer. There is also the problem with dual controllers (not sure how USB/firewire/whatever next technology is works with handling 2 controllers at the same time) using the processor.