Rules are not changing and have not changed since May 27th 2012. Inside the guide in game (menu > guide button) is a section on gang rewards. It states that a gang with 4000 hours get a gang base (5 rooms) with a 'grab hat'.
Previously, before May 27th 2012 a few gangs (GEGS or GETS (always get confused between the two) and Obsidian) ended up with another set of hats (which I assume was at 4000 gang base hours), however since said date this hasn't happened with other gangs.
The iFreeze hang out was finished today. I apologies for the delay.
There are also two new rewards coming to the gang rewards-
At 10,000 gang base hours a new hat (if a gang doesn't already have two hats) get to give out 10 new hats. (Can either be a new hat, or one of the existing hats the gang has). However, if the gang already has two hats (as said above, Obsidian and GEGS or GETS) they will have give out the existing 2nd hat. Since 6 are already out, only 4 members will get this.
At 15,000 hours a gang will have their own gun skin. If the majority of the gang use M4 (the gun choice is based on the leader, which I assume they would go with the gun that their gang use the most) can have their own gun gang skin. (It will be a gun with their name on basically, and yes the players before buying it will need to already own that gun)