So what can they do now? If they lock 270 (which I'm sure they will) and make crafted accessories have only one substat, then raid drop VIT will be the best by default. The problem with this is it's dumb and means that tanks will just have 25 AP in that slot for the entire expansion. It also makes future raid drops not feel like upgrades. I see a few possible solutions
You get STR upgrades on left side gear from raids, you're fine. Besides tanks job is to absorb damage, dealing it is just an afterthought.

You're tanks not DPS, and raids are calculated based on basic tank damage output in tank stance nd DPS's damage rotations. Healers damage isnt taken into account, and obviously raid will be balanced around tank DPS in full VIT gear. So don't worry, babe.