Oh come on, there's no more room for filler.
Lelouch has to destroy Britannia, fight Schneizel a couple times, face the Emperor, learn about his mother, and get his HAPPY END with Nunally, Suzaku, and possibly a member of the female cast. CC, VV, Kallen's brother, the Emperor, a good deal of the Knights of the Rounds, and Lelouch's mom's relationship with CC need flashback explanations. Not only that, but we need to fix the problem in China, get Nina's revenge on Zero, find out what Schneizel's up to with Nina's nukes and get the BAD END for Suzaku that Sunrise has been promising us. And somehow this is all going to fit together coherently in 17 episodes.
Filler would be suicide.