EA have announced the very first big change coming to the game, which will be the first of several to arrive eventually. The Gunner has had his three abilities overhauled; live this fall.
The 'grenade', which is actually an explosive keg, now will not only inflict damage to foes but also slow them down some. When frenzy fire mode now activates it also heals the Gunner, and will heal more if you down some enemies. Finally, the shield mode affects nearby allies.
The changes to Battlefield: Heroes will be going live this fall.