Something like that. They should get lots of different bonuses, but i think there should be specific weapon replacements, like attachments.
Actually.. I think there should be tiered perks. Like 3 different perks after you choose support, which give you your support perks bonuses plus that specific perks, and it's the 3 tiered perks that have the replacement stuff.
Like say when your Commando perk reaches lvl10, you will unlock the sub-perks at lvl0 and automatically start leveling your 3 sub-perks.
So those sub perks would have specific requirements the others don't have.
Like choice1 for the akimbo deagles would level from pistol kills. The getting scope for bullpup would level when you get kills with bullpup from very far away. Getting the big mag and bibop would be from.. I dunno, something unique the other perks don't use.
It's sort of like TF2 there with the replacements things. That little known valve game..
Support choice1 :
Tripwire claymore mine (replaces grenades) You could place more depending on perk level.
Pyro choice1 : Incendiary grenade (replaces grenades)
Marksman choice1 : Deplete uranium/titanium bolts for crossbow(pierces [better?])
Medic choice1 : Upgraded syringe which can be used on the enemy to make them act as an ally, attacking specimens for you. It would drain all your syringe's "ammo" and add a delay before it recharges. So strong on FP's if you get it off without dying. ^^
Medic choice2: Ooo a semi-auto teargas/zedgas grenade launcher to replace the rocket launcher.
Berzerker choice1: hm don't know.. a stun or snare thing sounds good though. Like barbed wire, but barbed wire should slow you too.
Commando choice1 : Akimbo deagles.
Commando choice2 : Scope for bullpup.
Commando choice3 : dual drum 100round mag and bibop for bullpup ( like
[url]http://www.project-x.org.uk/images/picsa80cmag.jpg[/URL] ) or a gun replacement that replaces it with a 5.56 or 7.62 MG.