I like having a poll, I think it provides the devs with insight into what the players are looking for a specific feature in the game and I'd like to see more polls like this covering different features. So here's my two cents.
What we are basically talking about here is cover and concealment which are not the same thing and I imagine from a strategy game like this has varying difficulty in implementation. Cover provides you with protection while concealment just prevents the enemy from actually seeing you. A shrub provides concealment since if I fire into a bush and you happen to be hiding behind that bush there is a statistical chance I will hit you. If I fire at bulletproof glass that I can see you behind that offers no concealment but a certain level of protection which brings about two new topics which are penetration / damage and hit location so I'll save my opinion on those for another post :). Let's assume for this discussion that for concealment you are either seen or unseen and for cover we have four levels (25%, 50%, 75,100%) based on how much of your body is exposed. For hit location you are either hit or not.
25% - I'm standing behind a wall knee high
50% - I'm standing behind a wall that is waist high or crouched behind a log
75% - I'm standing behind a wall with only my shoulders and head exposed
100% - I am crouched down behind a wall in full cover and fully concealed
Without taking penetration and damage into account you could get some pretty easy calculations for chance to hit, however to me it's still missing some realistic relevance here. I think penetration / damage would be way top difficult to implement in a game like this (but I could be wrong) since you then have to determine what the material of each cover is and assign it a value then determine the bullet size ant type (Ball, AP, Explosive), etc, etc. However I think implementing a hit location would bring you a lot closer to realism while providing the feature of hit effects based on location (I'll go over that in one of my other posts)
Now if it is possible to implement penetration and damage then I'd say go for that too since it would only add even more realism to the game.