each specialization line has a progression bar that is filled up as a player participates in combat. at any time a player can activate a specialization, at which point, however filled up it is, determines how many traits are active. specialization regression or full loss of progression can be caused by any number of ways (not fully determined yet).
this could be a profession mechanic that can allow a profession to a have more than three specializations fully active or partially active.
or have a fourth or more specialization that is progressed while the other three are always active. this could be worked around in many ways.
only one or two could be active always while others need to be progressed…
max specialization progression could trigger other things also as another mechanic…