Every class has vit + their own main stat on left side gear (as does tank). All non tank class accessories have their main stat (which effects damage output) + 2 secondary stats. Currently the "tank" accessories have 2 secondary stats and vit. If SE rolled out a new "tank stat" I would assume that tank accessories would follow every other class and have the main stat + 2 secondaries (again, future gear)

Every class needs VIT. As it has no effect on damage done, or really anything other than HP totals, I don't consider it a main stat. SE would likely need to add VIT to left side tank gear to make a new stat work.