Just two ideas I've had since the early days of CoV. The names are crap but I believe the concepts would be fun to play.
Tactician: Near identical to the Mastermind AT but instead of support pool secondary, they get control pool secondaries. Focuses on damage mitigation through enemy disables.
Inherent- Attacks of Opportunity. Pets do additional damage to mobs affected by some sort of control power, with different bonuses for different controls. So a small bonus for immobilized mobs, scaling up to the highest bonus for sleep targets. The bonus stacks with multiple effects on a target, like held and immobilized. Also keep the bodyguard effect.
Assaulter: Diverging from the normal MM AT, Assaulters pick a ranged damage primary and a pet secondary. Their primary focus is as a glass cannon. Overwhelm their targets with mass damage before the enemy gets a chance to take them out.
Inherent- Group distraction. AKA "He did it." Aggro the Assaulter generated redirected to their active pets, split evenly.
Pets as a secondary would require some alteration of the pool.
First, relocate the pet summon powers so they are available at the 1, 16, and 28 spots. Keep the extra first and second tier pets showing up at 6, 18, and 24.
Second, keep the upgrades where they are so they unlock at 10 and 38. Maybe move the second upgrade to the lvl25 spot, but that would push the bonus power previously unlocked at 18 into the 38 spot.
Third, the three attack powers get replaced with theme compatible buff or recovery powers from buff sets. Something to help keep the pets going during and after battle but not stuff that distracts the from the primary pool. Like empathy's single target heal, AoE heal, and mezz protect for soldiers. Or warmth and the two fire shields from thermal for demons.