I was super pissed that Grunt wasn't a squad mate in Mass Effect 3, so I came up with an idea for him to be in the game again.
After Attican Traverse: Krogan Team, Wrex or Wreav can mention that he is in the Med Bay, so Shepard can then go down and have a talk with Grunt, after a little conversation Grunt can then say that he would like to rejoin Shepard but he would be okay with fighting somewhere else, Shepard can then choose between letting him aboard(Paragon) or telling him to join the war effort(Renegade).
If he is let aboard, then he can either have a samall argument with Javik(if recruited) but then go to the Shuttle Bay because he was tired of his old area or just go strait to the Shuttle Bay for the same reason.
His powers can be Carnage, a grenade power(Inferno or Frag), Krogan Berserker, and Incendiary Ammo. His weapon training can be shotguns and assault rifles.
How awesome would this be, Grunt is my Favourite squad member Ever, so it would be fantastic if this DLC was coming soon.