So this is a concept i want to introduce, what specifically goes into the additional tree is a debate beyond this suggestion but here it is!
We create a new class tree separate from the existing class tree's (in a similar way to which FRS operates now) where players taking specific combinations of Master boxes grant access to those skill boxes. We could use this to enhance specific combinations of classes for both balancing and improving the abilities of somewhat limited support roles
Here is a basic example. You reward a master doc, master officer by granting access to the enhancer tree. Lets say you have 5 points to spend for 5 boxes. These boxes give bonuses up to a "master" box that has a significant bonus
Examples of the rewards in the boxes could be things like. Group buff duration, healing potentcy, rez cooldown etc all in different trees so the player chooses what kind of enhancer they are. Finally the "master" box gives an added bonus. That could be something like an extra heal skill, an extra rez skill, a new stance buff, a new group enhance buff (these things are all for debate just trying to provide concept)
you could pair specific master boxes to do each of these trees, a tank one could grant punishing blow reduction, or armor, or DR etc etc. I would suggest these bonuses should be aimed at group support rather than raw damage, even in the case of a DPS pairing.
Thats the concept in a nut shell. i'll be happy to discuss it in discord if you would like more examples or suggestions on it