The Playstation 4 will certainly have the capability to power multiple 1080p displays. Thus allowing for 2-4 screen multiplayer from the same box, at 1080P! Will it though? Good question. An interesting feature Sony may want to consider putting there. When you consider, that my Athlon 1640B, 2.7 ghz processor, running in 32-bit mode, can support 1080p, it's not hard to imagine 8 3.9 ghz cores, running in 64-bit mode, supporting multiple 1080p screens, even 4, especially with built-in vector coprocessors (AMD's APU). I might like to see this feature. Thus multiple players can play in different rooms, from the same box.
Further elaborating - it's not that difficult to do, for a system with enough cache. I.e. say 8 MB of L2 cache, and 32 MB of embedded RAM for the graphics chip. All the items that are sent over the memory bandwidth pipeline are stored on cache, and then sent 2-4 times to the graphics engine to be rendered. Thus, the main limitation, the memory bandwidth one, is not an issue.