There's no official release date set, yet I do know the 5th Gear guys have been hard at work. If Blake doesn't get on here, I'll ping on him about it in the next day or so.
As a general rule of thumb, they don't like to release it until at least Week 4 of the build season. They don't get the rules ahead of time, so that basically gives them 4 weeks of time to develop the rulesets/models/etc into the sim. It also gives plenty of time for teams to come up with their own designs such that they shouldn't be influenced by the designs they see in the sim. Quite literally, they've had to code in 'magic' to the simulation robots to get their nuances to work properly in the PhysX engine. Unfortunately, that just doesn't translate into the real world. Go figure
silly software guys get all the easy stuff.