Aye, it seems to me that a general "pool" of specialists would be a cool thing to have, so that you can build ad-hoc squads depending on people's preferences and availability.
Myself, I haven't really unlocked anything besides the Sunderer AMS, its ammo dispenser, and a cool pistol yet - but
once account-wide unlocks are in I think of dropping some of the
SC I have left from the Alpha Squad package on equipment (I'm really looking forward to replace my APC's second turret gun with that heavy mortar, for example).
For infantry combat, I still prefer the intense action and support significance of being a medic. I've lately learned that Infiltrators are rather fun as well, but that's not someting I would wish to focus on. Next up in terms of certs is the T1S assault rifle, which I'm going to kit out with some cool attachments like an underbarrel shotgun, Starship Troopers-style.