This being their first foray into consoles and all multi platform development was handled completely in house, they need to focus on getting the features they do have working properly.
Have you even played the SP? The AI is retarded. Nowhere near as smart or fun as Reach or Gears. They're really just barely more sophisticated then zombie AI.
The AI has to improve drastically for a Horde mode to work well.
Perhaps for Crysis 3