I'd love to be able to smash someone around the head with a shovel. Perhaps the shovel and pick could both be used though, with slightly different attacks, maybe a quick, low damage attack with the pick (possibly with 'headshot's that kill instantly, if the head is hit obviously) and slow, more powerful attacks (with no headshots). These would reflect their current uses, so I think would not destract from the realism.

The only vehicle this game needs is a boat.

I think the game should be split in two. This is gonna be long as fuck so bare with me.

Classic mode - Pretty much as it is now with minor improvements.

Hardcore mode - Basically as close to world war 1 as the voxel engine will allow but not sacrificing working well balanced gameplay for "Realism"
Below are my suggestions for hardcore mode.

1. Tanks - No tanks because it would just look silly as fuck and would ruin the pace.

2. Boats - As another player mentioned, all vehicles will pretty much ruin the game. Boats i think are the only vehicle that would fit in. Not much to say about them really, maybe carry 4 players max, have a really simple design (Think minecraft boat) and have no firepower whatsoever. I dont see water physics being implemented so i wont go further on this.

3. Biplanes - Some kind of planes implemented into the game, either non controllable or ai controlled with targets marked by players. Planes have a very low altitude restriction for more interesting gameplay( will go into more detail on this)
They spawn at something similar to the supply tent, with say a hangar skin and need say 4 blocks wide and 16 blocks long to take off.

If Player controlled planes are implemented they should do little damage to ground targets through very clumsy and primitive bombs. Basically a fighter bomber plane that doesnt really excel in either role, but can be very useful when controlled by the right player.
Perhaps a mounted machine gun that does very little damage per bullet and ends up being only as or a little more powerfull than the infantry rifle.
Players could also use this to manually scout the map and mark targets themselves through team chat.

If the plane is ai controlled, there could be 2 branches of plane. Scout and Bomber. Both have little fuel so return straight after their objective.

Scout - can see around it in a small radius marking targets on the map similar to what happens when the intel is returned, only above ground of course.

Bomber - Inaccurate small carpet bomb effect, guided by players marking targets, perhaps with a certain block or throwable smoke grenade. (Vulnerable to griefers though, hmm)

Both have a reasonable respawn rate and can be sabotaged by destroying whatever spawns them.

Both can be shot down relatively easy by players focusing their fire on them.
Players could also imitate the barage baloons of world war 1 and 2 by constructing large towers of blocks that the planes will either fly into (if ai controlled) or simply avoid (if player controlled)

http://www.fiddlersgreen.net/aircraft/Balloon-eagle/IMAGES/barrage-london.jpg

Artillery - Basically this, pasted from another thread.
1. Cant move from its block except up or down
2. Can shoot halfway across the map
3. Always somwhere right near the back of the map
4. Slow reload rate.
5. When used gives sumthin like the ironsights?
6. Destroyable/slow respawn rate .

Classes - Havent really thought about this but i think it does need a basic class system, something like this.

The good with people deuce - Gives ammo, medical supplies/can heal. Maybe give a boost of some sort to surrounding deuces within a small radius. Has appropriate defects and or weapon for his class.. Can only be chosen in a squad and can only be one in a squad (Read next part for squad mechanics)

Builder/Sapper/Destroyer deuce - Has more blocks, more effective demolitions. Has appropriate defects and or weapon for his class. Not sure if it would need capped. Can build supply tent and rebuild/repair destroyed artillery and hangers.
Can carry more blocks than other classes.

Soldier Deuce - Same as now, with some minor adjustments perhaps.

Heres 2 changes i think should be made to the games core design as well.

1. A squad system like battlefields that highlights people in your squad on the map, along with a squad chat button.
2. Might be going a bit too far here but maybe a grid overlay button that puts a grid over the map and allows you to point things out to your team a little easier.

I have a few other ideas but i feel like they are kind of restricted by griefers. The games design allows so much but at the same time it gives so much for griefers to completely destroy as well. Such is life on the internets.

I think biplanes should be strictly used for surveillance like it was in the earlier parts of WW1. Thusly they could go high distances to make it difficult to shoot down and capable of giving intel to your allies. If they had weak guns the airplane would be too nerfed to want to be used especially with a low sky limit.