Haven't watched much X-Com 2 stuff yet, but watching X-Com 1 streams I gotta tell you-
I wish they added friendly fire! That'd make the game more fun and add another thing to worry about.
Friendly fire is possible with panic and mind control. In the X2 streams you can see panic spiral situations where one soldier on overwatch panics, another soldier panics and runs out of cover, the overwatch shoots the runner. Or a panicking soldier lobs a grenade into his squad.
Well, of course I know about that.
In fact, in my latest vanilla X-Com Iron Man Classic game it ended when I was doing a Council mission and my guy who was in full cover, hunkered down, inside smoke was hit by a Thin Man, panicked, then shot the VIP we needed to rescue. I was mad.
What I mean is when you have soldiers standing in a conga line and are shooting through each other there should be a chance to hit a friendly soldier. Here is a diagram:
A SS
S are soldiers, A is an alien, they are all in the same horizontal square. The second S, when shooting the first alien, should have a chance to hit the first S, like in X-Com, the original.