I remember being promised this! Where art thou o’ shiny ball!
The Grifball gametype is being tested, tweaked, and changed accordingly to what the Grifball community ultimately feels like will be the best overall version. With the initial gametype(s), maps are also being created to fit into this playlist. When everything is done in the testing phase, the gametype(s) and maps will then be submitted to 343, and therefore will also need to be approved by 343, so it can go into matchmaking. Be patient. I think we are coming close to finding the most balanced version of Grifball in Halo 4.
If you need some of your Grifball thirst quenched, head over to grifballhub.com.