This is something that I have brought up numerous times during my 18 months with Dirty Bomb and I feel I need to do it again because in that 18 months we have seen what, a couple of tiny bug fixes that related to dying and being revived on them (that still did not completely work).
Right now the MG Nests are possibly one of the worst designed additions to Dirty Bomb with horrendous handling, even worse sound, poor visibility and simply broken collision boxes. I personally play Dirty Bomb on between a 70 and 75 field of view yet still struggle to see if a MG nest is manned until it starts shooting at me. I can literally stand still, move my head closer to the monitor and start reading pixel by pixel and still feel like I am guessing if they are manned or not. Obviously this is something that is made much worse by manning them with smaller Mercs (especially Aura) but I still sometimes struggle if it was Rhino on there.
Just when you thought your experience could not get any worse, you soon realize that if you have the MG Nest out of sight, then the battlefield better be close to silent if you want any hope in hell of actually being able to hear it shooting. Honestly, when I die to the MG Nest and I was not fighting vs the MG Nest, I find myself being all like “OMG WTF WAS THAT!?!?” and having to wait for the ghost to inform me.
Even if you could get over the horrible visibility and sound design, you still have to then contest with the fact the MG Nest is willing to eat basically anything you throw at it. Something that is only made worse by the fact that the vast majority of MG Nests in the game are perched up high meaning the angle you have to put damage onto the Merc using it is all the more frustrating. I can frequently use multiple full magazines to even kill the squishiest of Mercs that are on it. Even when sniping you will often watch your bullet simply vanish even if you know (and can watch it back on video) you never hit the MG Nest. Also, countless times I have used airstrikes, artillery strikes, Naders nades and Fraggers nades and watched them land 1 foot from the target and do 0 damage. That said, good luck even managing that due to the nades collision being based of what seems like the characters collision. Most of the time you throw your nade and watch it bounce off nothingness right back at you.
So you can get past all this???
What about the horrendous collision meaning that if you are around a MG Nest you feel like your movement is being constantly screwed with? The collision boxes on the MG Nests are huge, the volume must be at least 5-10x what they should be and cause major frustrations and inconsistencies when it comes from getting from A to B. They trap you in corners, block your route and make simple navigation a real pain in the ass.
Still not enough to get them removed or completely reworked???
The final point I am about to bring up just sums it all up really. Even when using them they feel, look and sound so underwhelming. Sure they are very strong, maybe even too strong but when you are using them they feel like an RNG cannon where you simply point and click where you hope the bullets will go and pray. One burst, 6 headshots instant death, next burst 30 bullets all on target with a couple of feet taps. They are restrictive, slow, RNG driven, feel janky and look super placeholder.
Sure it will change certain sections of the map and other things may need in future to be tweaked to compensate for them missing but I would do almost anything to see them removed. I despise them so much! In my opinion the worst designed thing in the whole game! They are the kinda quality you would expect from a student project, yet they are still here 
EDIT: I would also like to add that since the changes to the spawn shield mechanic, at least 5 of the turrets at some point shoot onto people that have spawn protection and the reduced damage shield making them fairly frustrating to use.
Also, the a lot of the positions currently work in a rich get richer kinda way. Especially the turrets on at Chapel and Trainyards second and final objectives. Being able to use this these turrets is only really possible once you already have a solid hold on the attackers meaning that in a balanced match they are almost useless but really come in handy for doing a complete pub stomp. This is due to just how vulnerable they are to a attacking sniper and as we all know attacking snipers are only really able to apply pressure if their team is already in a fairly decent position.