I believe that mountable machine guns and mortars should be implemented in game seeing as this would a more strategic side to the game and i know that the following ideas of mine will need a lot of work so isn't that what forums are for? Debating until we get an idea everyone is happy with?
For the Mountable Machine gun, i think that the only way to fire it is to well... mount it to a block from either 1 block high (doing this means you can't duck for cover whilst using it.) or 2 blocks high (giving them the ability to duck down) and that it should contain about 400 rounds in total giving it 80 rounds per mag meaning it gets 5 mags before needing another load of ammo to counter the problem of base camping. But it should also have a means of getting ammo from team members, for example one or two team members re-spawn, they go to the capture point/ base tent. But, instead of just being able to replenish your guns ammo and your health you would be able to to press a key such as "p" and a window would appear with 2 options (this linking slightly with the mortar now) to choose either Mg ammo (Mountable Gun ammo) or Mortar ammo and that the player can only carry either one and only one of them in which they have to deploy before they carry any more. Now, to Deploy it would be as simple as placing a block just click where you want it. so that you could build up ammo stores, or you could place it next to the Mg and it would take up the ammo filling it with 160 more rounds (2 mags). This also means if the gunner and any defenders get overrun the opposing team could take any ammo that has been stored in the area as simply as pressing "p" to pick them up or just keep it their for their own gunner. Also, when the block below the player is destroyed the player falls and the Mg gets placed back in their inventory ready to be placed again. One other thing for the Mg is that if a player wishes to move up with the rest of the team they just press a key like "O" and it gets placed back into their inventory. This also removes the problem of the opposing team stealing weapons if the only way to get off them is to pick them back up. If a player gets killed whilst using it the Mg will be destroyed along with the player. Now for the fun bit. The Mountable Machine Gun should have in my personal opinion a slower rate of fire than the Smg eg: say if the Smg's fire rate is 5 bullets a second the Mg will be 3 bullets a second, But don't worry! The Mg's power will be a bit stronger than the Smg for example say if the smg kills in 4 hits it will kill in 3 only it wont be as accurate no because of spread but due to a large amount of recoil. I mainly see its purpose to be Support, Defense or Heavy Assault.
Now, for the Mortar it's a similar story, I'd imagine it would contain 12 rounds before in need of reload have quite a long range and be as effective as a grenade, although it wouldn't be able to hit the others team base from the other base and it would be rather inaccurate mainly used in a group of 2-3 to support advancing troops, But a more accurate mode would be available this would be done by right clicking (aiming) and you would get an angled view of the mortar barrel with a little site at the end and a HUD display of what angle your aiming at, one downside to doing it this way is the range is greatly decreased but the accuracy greatly increased, perfect for eliminating very successful snipers preventing your troops from moving up. Yes this weapon would also have to deployed and need a large amount of open area to work efficiently eg: 9 block minimum with chances of mis-fire if its about 2 blocks deep to avoid this an 18 block wide and 2 block deep pit containing 2 mortars would be efficient maybe with one side having higher fortifications and the side your firing at just the open pit so you don't mis-fire and end up shooting yourself. I think this would also be useful for Support and Defense and in a indirect way Assault as well.
If these weapons are introduced i also think a sidearm as a choice to replace the grenade will be handy for these weapons maybe just a low powered mid ranged fairly accurate pistol which takes about 5 shots to kill or 2 in the head to kill so that when moving up the Mounted Machine Gun users or Mortar users can fight instead of being sitting ducks.
Thanks for reading, Nyazzle