AoS is very different form other multiplayer FPS due to its building system. To make it really deeper in gameplay I have some possible suggestions of how it may be done. I strongly doubt if any of these ideas look possible, because they will require a lot of coding and testing, but still...
The ideas below radically change the gameplay so they can only be implemented into a special game mode, contrary to "classical" one.
1 .Inventory and stamina system.
For everything below, an inventory system must be implemented. Everybody has three slots which can be filled with either common weapons(1 slot, 2 max), special weapons (2 slots), heavy special weapons (3 slots), usual blocks (either 20 blocks, if a player has a weapon, or 50 if he has none), tough blocks (10 ones and it restricts a player from using weapons), ammo boxes, 3 grenades, or a demolition charge. Explosives and ammo boxes doesn't influence player's encumbrance. The loss of stamina depends on the number of filled slots, and its regeneration depends on player's health (x3 difference from 100hp to 1hp). So filling all of the slots with weapons or blocks, the player risks to become vulnerable, while a light-foot saboteur can be a pain in the ass with only an smg and some explosives. A player can throw away weapons and take them.
2 .Different block types.
You can choose between expendable and numerous but fragile blocks and a few very tough blocks. Like earth (for impromptu defences) and stone (or concrete, for foundations, long time buildings, they are placed with a delay during which the builder is stationary). They are distinguished by texture(i don't know if it is possible with voxel engine) or color (this way colors are locked).
3. Special weapons.
Powerful weapons that are capped to 3 per team. After a player wielding this weapon dies, another one is supplied to base after a small cooldown. Make running very problematic, increase stamina loss three times, have a slight speed penalty. One can't carry a special weapon with a normal weapon at a time, even if he has enough space in the inventory.
They can still be supplied with ammo from normal ammo boxes.
3.1. Light machine gun.
Basically it's an smg with 1,5x rate of fire, higher recoil, higher bullet speed, and it has a 5% chance to penetrate a normal block. If this happens, the bullet damages anything up to 2 blocks ahead. Has 2 clips of 100 rounds.
3.2. Anti-materiel rifle.
A rifle with a magnifying scope, very accurate, has a 50% chance to pierce a normal block. A direct hit scores an instant kill, but if a target stands behind a block, it only takes half health. No clip, every round is loaded separately. 4 seconds reload, 20 rounds.
4. Heavy special weapons.
Long time defences may be reinforced with stationary heavy weapons. A few of them are spawned undeployed at the base at the beginning, and also at the strategic points like bunkers or towers. All of team weapons need to be carried and deployed in a desired location, and may be captured by an opposing team, packed up, and carried away to be redeployed or hidden. They can also be destroyed with explosives. If this happens, a new weapon is spawned in the base after some time. Ammunition needs to be supplied from the HQ and consumes inventory slots (A "chunk" contains a said number of ammo, and can be placed and destroyed) Weapons which doesn't belong to any team can't be unpacked and have unlimited ammo. There is a cap of 2 special weapons per team.
4.1. Heavy machine gun.
It has twice of smg's rate of fire, bullets fly much faster but with a bit larger spread, a limited firing arc and turning speed, can overheat, doesn't have clips. Has a 20% chance to penetrate a normal block similar to a light machine gun. 500 rounds.
4.2. Mortar.
With hard blocks almost invulnerable to conventional firearms (grenades and special weapons are a little more potent), they can considerably damage even concrete blocks. 10 shells.
5. Ammo boxes.
During an intense action, ammo runs out fast (assumung that the max amount of ammo for each common weapon is reduced), and constantly returning to base is time-costly, there is a stash of ammo boxes at the base, that can be carried from a base and put where necessary. Ammo boxes use 1 inventory cell. A player must get close to a box, activate it and wait for some time to have his ammo replenished. After some full ammo stocks were taken the box disappears. There are three types of them: a box for all common and special weapons and two boxes for HMG and mortar. Heavy weapons ammo boxes work another way. They need to be placed onto the block where the special weapon stands, and it its ammo will be replenished. All ammo boxes can be destroyed with any weapon.
6.Explosives.
As an alternative to grenades (3 per inv. cell) there are demolition charges (1 per cell). They are devastating against blocks, but have a lesser explosion radius compared to grenades. When a demolition charge explodes underground, the tunnel celling collapses in a certain radius, and its possible location is displayed on a map as an expanding circle. A special warning sound is played if it is explodes close to enemy base . On the other hand grenades are very effective against personell, but do only minor damage to blocks.
Thank you for reading. I hope that some of these ideas may be useful.