it's neat idea, but units all go through the same training, so they are all pretty much equal in skill, and really only differ in their roles, so you wont likely find a varience as such where one shoots better than the other, perhaps only when someone is handed a weapon without any training and expected to fight.
The real difference comes with experience, veterans have more experience, and as such can read and predict a battle better than a "noob" in order to make the better judgement calls on the field with the right tactics, but then it only affects the tactics used since the lesser experienced may probably not think 2 or 3 steps ahead.
So really, I can't say I am in favour of variety of skill since it will really differ so minimal, that it wont really be worth doing.
The rank markings however, VBS has that, and it isn't a bad idea. If you could somehow determine who a squads leader is and gun him down, you could break the squads moral and performance, as well as their ability to work well together, then again, there will be someone else next in line to take charge, so it should weaken the squad none the less since it's lesser experienced members taking over, but i dont know if it will really be worth implimenting that much since you could pretty much wipe a squad out before they even realize what happened.
As far as the skill level goes, i think that is pretty much worked in already. However it would be neat if th player could be locked to a skill level instead of being a jack of all trades. Disregarding basic stuff, the special role skills is what I am on about. Say if for example I am support gunner, it shouldn't really be possible in game to now be able to fly a chopper, or pickup a sniper rifle and wipe out an entire squad as if I am a sniper, or heal my team mates as if I am a profesional medic. Agreed it shouldn't be rocket science to be able to pickup and operate a sniper rifle, or AT launcher, or bandage a team mate, but I think the player should be penalised somehow for stepping out of their role, and the impact must be negative enough to force the player to play the role he was assigned to do, but also not too negative to make it seem impossible.
Well thats my 2c worth.