Again, if they could make the smart ammo like in ME2/3, that'd be great, but I strongly doubt they can scale the tech up from infantry small arms to vehicle auto cannon level.
I actually doubt they could make the Cain work - if they could, it'd be a great FUCK YOU BETA weapon, and an awesome grenade launcher equivalent, but that's
if they can get it to work.
As for ME Assault Cannons, the main issues are that overheating is a problem - we see TSFs engaged in
Final Protective Fires, where they're holding down the triggers and unloading all of their ammo into the BETA - this isn't going to work with guns from the Mako and Hammerhead, because of the cooldown time required. I could see those in a support role, assigned to a Gun Sweeper acting as a machinegunner equivalent, but not as a frontline weapon.
tl;dr, any mass accelerator guns are going to be so rare, they're going to fit the same category as the Type-99 to start with.