Overall I really like all of these suggestions, but I have one main concern. I think making fortifications like sandbags and barbed wire completely indestructible to non-engineers could cause some gameplay problems, especially when combined with the ability to stack sandbags two levels high.
Let’s say I’m attacking a point but the engineers in my squad are dead, I have no remaining explosive packs, and I encounter a hallway that is made impassable by double-stacked sandbags. Now I have no options whatsoever for getting past them? I completely understand this is the point of fortifications, but I think we should always have some kind of option even if it’s very sub optimal.
What if, for example, instead of non-engineers not being able to destruct fortifications, they could still do it but only at 1/4 the speed? (Or even slower might be fine.) That way, the fortification is still very effective at hindering an attacker, and makes him vulnerable while trying to get through. But the player is not completely and permanently blocked.
This would also give us an option for dealing with teammates that build poorly placed fortifications either intentionally (trolling) or unintentionally from inexperience or bad decision making.
Those are just my thoughts. To reiterate, I really love these ideas, and even without my suggestion I think they would be a big improvement over how the game is currently.