Very nice work, it's pretty annoying that a lot of the vet abilities are boring and rather pointless right now. The 251 halftrack, SU85, and SU76 have pretty bad vet abilities too, maybe those could be reworked?
KV1-KV2-KV8-IS2:
ATM i can think of something that wouldnt tilt too much the balance or performance of the unit while remaining logical to what it is expected from the unit.
Here are a couple I thought up:
KV-2: 152mm Barrage- Fires three shells out to 100 range. Can only be activated when deployed in artillery mode. 80 munitions. Short cooldown, so you can make use of the hundreds of munitions Industry tends to float.
KV-8: Flame-wall- Shoots a wall of fire in a 45 degree cone for 10 seconds- think dragon tank flame wall from cnc generals. 60 munitions. KV-8 cannot move for the duration of ability.
KV-1, IS-2: Man the Guns- Rate of fire increased by 30%, movement speed cut in half. 50 munitions, remains active continuously until deactivated, much like Take Aim on the 57mm.