So, what? You pull a "for the motherland!" and trade a half-dead paralysed rookie for a reset of panic and +20 will for the whole team? Can you add permanent buffs from abilities? It might be fun to give the Commissar +5 will permanently for every field dismissal.
Still not sure on the exact details. The challenge is going to be making sure that all the different abilities will avoid overlapping to much, and that they don't become overpowered. For example, I want one ability that can be used to give each soldier in the squad an extra action. But I don't know if I want to attach it to the execute ability, so that the price is a life for each activation, or if I should make it a stand alone ability, with one use per mission, or if I should do both. I also want to make a solace like aura around the commissar, because who wants to panic around that guy when panicking will get you killed more effectively then enemy fire? But then I run into the problem that that would overlap with the commissars execute ability, which at its base would give a will bonus and a clear to any mental effects.
My rough plan for now is to make the base execute ability clear any mental effects along with a will boost for the rest of the mission. Then at corporal you can choose between an offense or a defense bonus, which would both give +20 for two or three turns. Miscellaneous abilities would be a squadwide inspire ability, and an aurora that would remove panic. The lower ranking abilities would be what you would use on a squad of rookies and squaddies, powerful bonuses that turn what was otherwise a code black into a victory- at the cost of a life. Higher ranking abilities would be one that you would use to support an actual squad, with passive bonuses and abilities that aren't as powerful, but don't require an execution. That way the commissar would be relevant as more then a joke soldier. Suffering lots of casualties and can't get a good squad together? Train up a commissar, get him one or two ranks, and give him a squad of rookies, and while you won't suffer casualty free missions, you will get a couple soldiers through it alive with promotions. Later on, he'll still be relevant, just not what you base the squad around.