How about a Training Facility?
Have it be a new buildable facility.
You stick your soldiers in it for a month. They improve slightly. Maybe make it dependent on researching a new tec or medkits. The improvement would be less than a good combat mission.
I would make a Mark I, and Mark II.
Mark I would only improve some things (strength, Stamia, health, Time Units, Firing and Throwing accuracy) by a little. It could improve 1 stat or improve several stats by a small amount.
Mark II would improve everything (Except psi strength, maybe psi skill), including bravery and reactions. Mark II would help improve more stats by a larger amount. Obviously, psi skill would increase by a smaller amount than a psi lab. It should require psi labs be unlocked for research the Mark II.
If I was writing the flavor, Mark I would be described as the most modern gym/firing range. The Mark II would be that plus psychological testing and a VR facility that uses psi.
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Also, in the skirmish mode, can we have a training bar for our soldiers like the aliens have a tec bar?
It would be cool to have elite troops try to kill mutons with just rifles.
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This mod is great, I especially like the skimish mode.