Well according to Guns and Holsters, some of the new M-15s will be chambered in .223 Wylde. Here is a technical note by Armalite. It says that the Wylde aka Modified SAAMI Chamber is better suited for 5.56 Nato match rounds and improved accuracy.
The 3-Gun M-15s will be sporting their own tunable muzzle brake. They also come standard with Timney Triggers set at 3lbs. They will be kitted out with light weight Keymod handguards. Not word on price yet.