A few years ago licensing was all the hype in the FPS genre, how many games weren't developed using the Quake/Quake2 engine ? But now every company seems to be building their own engine again (sometimes starting from the license obtained all those years ago, granted). It would seems that having an own engine is seen as a benefit, maybe because it adds an own unique look and feel to the game ?
Anyway, I don't think CA is willing to give up their beauty, especially since they are (probably) making another game based on the engine.

That said, Imperial Glory and The Battle for Middle Earth already LOOK like TW games (with less units on screen), and I wouldn't mind a Warhammer 40K: Total War.