A new Halo 4 reveal may be coming later this month. Finnish magazine Pelaaja is reporting that Microsoft will hold a Spring Showcase on February 29th and that a Halo 4 reveal is coming.
For now, nothing has been confirmed and this can only be taken as a rumor. Microsoft does typically hold a Spring Showcase in San Francisco ahead of the Game Developer's Conference, and this year's has already been announced, though Halo 4 hasn't been mentioned in connection with it.