I used to think about that too. Here’s how I imagine it.
Melee Warrior — Tal’darim — Votary
The unit mechanics offered by the topic starter works for me, but yeah, the “Votary” name should be more fitting.
Ranged Warrior — Tal’darim — Slayer
This one is already present in Co-op at Alarak’s army, so nothing more to elaborate here.
Cloaked Warrior — Purifier — Griefer
Cloaked just as others, but has no active abilities; instead, explodes on death, damaging all surrounding enemies.
Robotic Assault — Purifier — Disruptor, baby!
Well, you all know this one from the ladder. In campaign, though, I’d add something more to it to make it more attractive compared to the other big guys. For example, his ability to charge self and deal huge damage to the enemies nearby — just as it was back in the LoTV beta.
Robotic Support — Nerazim — Accumulator
Can recharge other units’ energy for the cost of own, also can create a cloaking field around self (similar to Vorazun’s Dark Pylon in Co-op).
Starfighter — Tal’darim — Scout
You know this one, right? The light flyer with a huge anti-air attack and poor anti-ground attack. Well, in campaign there could be added an AOE-effect for this anti-ground attack, so it gets decimating against ling packs.
Psionic Warrior — Purifier — Recreator
Similar to High Templar, but mechanical (obviously); can disable enemy mechanical units (like terran ghost in SC:BW) and also can restore HP to friendly mechanical units in an area.
Robotic Siege — Nerazim — Decimator
A Reaver-like machine which attacks in a straight line ahead of self, damaging all enemies in its way.
Unfortunately, I’m out of ideas for the Purifier Assault Ship and Nerazim Capital Ship