I want to start off by thanking the devs for all the hard work you have been putting into the division. I've loved the game since I started the day after 1.1 released. I think I see where you are going with classified gear sets and making a class system without locking a character to one play style, I want to add a bit more to that.
My idea is to lock the ability master mods and unlock them by specializing/mastering a skill tree. For example specializing in the medical tree allows you the Insta heal from destroying your own station.
Other things could be added to it like, the tree you specialize in gets a buff to points applied so 35-1 instead of 30-1 kind of thing. Some QoL/fun things to add to this is making the support station, turret, ballistic shield, mobile cover and my suggested gun shield skin able with weapon skins. Also make the support station, mobile cover and turret able to be picked up and placed elsewear only if they specialize.
Adding to that I propose a 4th skill tree based on weapons. Move pulse over to it since it buffs weapon damage, it shouldn't be in the medical tree. Replace it with a scan that marks friendlies and gives a heal over time or marks enemies and heals team mates per bullet striking a scanned target (it will have to scale with rpm so high rpm weapons don't heal more than low rpm weapons)
Second skill is a gun shield, it unlocks with the ballistic shield. https://www.everydaynodaysoff.com/2013/08/05/ballistic-shield-for-operators-only/ I could definitely see a version of this in the division.
Third skill is a Grenade launcher that unlocks with the sticky bomb.
The 4 skill trees can scale with different stats. Medical and tech scale with SP, security scales with stamina and weapons scale with FA. This would also help with match making as it can look for one security and one medical specialist and then fill the rest with weapon or tech specialists.