I've been playing World of Tanks for about a week now. With 364 battles under my belt, or a bit more than double my 5th Edition 40K experience, I'm starting to crave some changes to how vehicles work in 40K. Here's my accumulated thoughts.
1) All 40K Vehicles Should Have A Movement Stat
Why, oh why, does 40K treat every vehicle the same in terms of movement? Why do we only have a couple of ways (Fast Vehicles, Lumbering Behemoth) of differentiating movement? Having a stat would let us have additional tradeoffs when fielding certain units. Want to get there fast? Take a Rhino. Want to stick a weapon on the Rhino (Razorback)? Then you lose 2" of movement.
So something like the following:
10" - Hellhounds, Grot Buggies, Wave Serpents
8" - Ork Trukks, Rhinos, Baal Preds, Fire Prisms, Devilfish
7" - Rhinos, Battle Wagons
6" - Land Raiders, Razorbacks, Vindicators, Hammerheads
5" - Chimeras, Hydras
4" - Leman Russes, IG Light Artillery (Griffons)
3" - IG Heavy Artillery (Basilisk, Medusa), Baneblades
2) Turning Should Slow You Down - A LOT
If your vehicle doesn't turn, you should be allowed to double your movement. If you do turn, you should have to go your base move and only get one 90º turn at some point during your move. Agile vehicles could be allowed 2 turns. While lumbering vehicles (Russes, Baneblades) could only turn OR move.
3) Terrain Should Affect Vehicles Differently
Tanks should never be permanently immobilized, except by an enemy shot. Instead, a tank that fails a difficult terrain test should only lose one turn of movement.
As for the tests themselves, they should be easier to pass if the tank is going faster, and harder to pass if it's going slower. Say a 6+ if you move 7+", and a 4+ if you went more slowly or started your turn in the terrain.
For light wheeled vehicles like Trukks, it should be a 4+ for going slowly and a 2+ if moving fast.
4) Tanks should be easier (and harder) to hit
For infantry shooting at tanks, it should be a +1 at long range (over half), and a +2 at short range. Immobilized tanks should be a +3.
For tank-on-tank, the bonus should also be +1/+2, with a +0 if you're within 6" of the target. Because when you're bumper to bumper it's pretty hard to hit unless the other guy isn't moving (+3). Tank Destroyers (Vindicator, Medusa), should only hit moving targets within 6" on a 6+. Because if a turreted tank gets that close to you, it's over.
For artillery-on-tank (Basilisk), it should be +0/+1 when firing directly. Because they're designed to hit targets indirectly. Otherwise they would shoot like Tank Destroyers.
5) All Tanks Should Have Ammo Options
Russes, Medusas, and Vindicators shouldn't just throw large blasts, they should also be able to shoot direct-fire armor-piercing rounds instead. It makes no sense that a Russ can't meaningfully hurt another Russ with it's main weapon.
So let's give them all single-shot anti-tank shells that can hurt other armor. A long-barreled tank like the Vanquisher could just be more accurate or have a higher penetrating power.
In addition to this, let's have different classes of AP1-like penetration. There should be shells that offer a +1, +2, or even a +3 to the roll on the vehicle damage table.
6) Damage Should Accumulate
Here's what I'm thinking. Whenever a vehicle is damaged (Stunned, Weapon Destroyed, Immobilized), the next time that it's shot, the damage roll STARTS from there.
So say a Chimera takes a lascannon pen to the front and is stunned (roll of 2). The next time it's penetrated the enemy gets a +2 to it's damage roll. Meaning that it only needs a 3+ to destroy the tank instead of a 5+.
That would go a long way towards making vehicle damage less random.