Some people asked on the CPL forums if Quake 4 could be the WT 2006 1on1 game. Sadly CPL had to give a negative reply on it:

"Unfortunately, I seriously doubt that id Software would even consider offering the CPL a license to use Quake IV. If they were open to it we would seriously look at it." - Angel Munoz

What is known that the CPL WT 2006 will have atleast one Team Game and one 1vs1 game. Rumors go that the 1on1 game could even be a non FPS shooter.