As the title suggests, simply mark the friendly emplacements on the map so that players can find them and use them.
I know there are players that build them just to use themselves, but there are also players that place them in the hopes someone will find them and use them while the engineer can continue fortifying.
Adding this feature in should not be difficult nor controversial, just common sense at this point.
Common sense never stopped us, and it never will.
Yep!
But I think they shouldn’t be visible on map when being used.
Perhaps changing the color of the icon when it is being operated? I don’t think that removing it entirely is necessarily a good idea.
From the engineers point, knowing what is being operated and where helps to figure out where additional emplacements and fortifications need to go.
It really depends how messy it will be on minimap. I think it could get a cluttered very fast.
It gets cluttered for engineers no matter what. That’s not really an issue once you’ve gotten accustomed to it.
Keep in mind, barbwire, sandbags, Czech Hedgehogs (defensive structures) only appear when you have a hammer in hand.
So standard infantry will only see the emplacements, ammo boxes, and med boxes.
Yeah, you are right. 
Display the ones not used in white (like we have with ammo and med boxes)
While used ones in blue.
While ones used by the enemy…