I doubt this is possible or it would already be in the game, but here goes: If a player was unable to shoot or take any other action after switching from one stance to another before moving slightly it would solve pretty much all of the problems with unrealistic movement. Insta-prone, insta-crouch, pop-up and shoot - all would no longer be effective. Then, the standing firing stance might actually see some use and suppressive fire would become a lot more effective as it would be much harder for the suppressed to return fire.
I think proning should be fast, real soldiers just throw themselves on the ground, but the standing up. With 20-40 kg equipment you'll need a few seconds..
-The Foreign Legion Engineers we trained with had an interesting way of getting down on the ground, from a walk/run they just tightened up their feet and fell like a tree, leaving them free to fire all the way down. You really have to fight your natural instincts on this one, I tried it a couple of times but always the urge to protect my face/torso got too strong and I ended up bruising my elbows alot. If you manage to ignore your natural instincts you won't hurt yourself doing this, it's when you do as I did that you hurt yourself.
the animation is, jump down, use your elbows to take the fall..So you can't shoot while hitting the deck...
Also IMO you can look about well too fast while lying down.
The side roll is just stupid... I mean, how is it even possible? It would make sense to have a roll animation while strafing when already on the ground - in fact, that would be great - but it makes no sense rolling while throwing yourself sideways to the ground. It is just physically impossible.
The day that the PR devs can announce to the world that they have cured the BF2 cancer of instant pronerolllaserfire will be a day of great celebration
How about using the animation( screen blur heavy breathing ) of when a round comes very close or standing next to an armored vehicle while it's shooting.
That would simulate the "stun" of bellyflopping onto the dirt and the blur might make accuracy more dificult.
I've a feeling that (devs correct me here) when the prone action begins, the whole animation is completely hardcoded into the engine. So short of creating an entirely new animation, there's nothing that can be editted.