I have been thinking alot about impact and armor. Armor as a keyword was powerful in the core box, but over time it has lost alot of it's edge.
Bigger dice pools, surge-crit, more aims and the new critical keyword have made armor a paper shield. Sure it's better than nothing, but you don't really need impact to take out a vehicle.
The armor keyword was also changed to include a number instead of blocking all hits. I think you can take advantage of this and make a new rule.
Suggestion:
"While a unit with armor is defending before the resolve armor step, if the attack pool does not contain impact, flip one attack dice with a crit symbol to a hit symbol if able".
This would be a small nerf to critical only lists and make impact a little more important. It would also help full armor vehicles more than armor 1-2 units, since they can only block so many hits.
I know the tactic is often to ignore heavies and that they aren't always point effective. This could be a step on the way though.