Having DX11 support for Planetside would be pretty useless I think. Most new cards dont get very good FPS at high settings in most single player FPS games at the moment (DX11) let alone in a game like Planetside with the huge battles and shit blowing up in your face everywhere you look
It could be they see it as a future proof thing, but I don't really think its a viable reason to delay the game for :P It's probably just some 3rd party software like Streambase or Havok or something.