343 is going to unlock them for everyone sometime.
"Sometime"??? lmaooo nice
In their own words, the other specializations will unlock one by one as the community achieves certain milestones.
...but they haven't told anyone what those are supposed to be, so we have no idea if we're expected to completely more Spartan Ops missions, or get more people to beat the Campaign, or max out certain commendations, or so on.
So for all we know, another specialization might unlock tomorrow, or it could take months before another one opens up for normal players.
"Wall of Text'D!" --- oldskoolplayr76 "POwned again." --- blight family