As a DK tank I can say nothing is going to change much in WoD compared to now.
I use strenght for both tanking and DPS
I ignore dodge/parry (and they'll be removed)
I roll on pieces with mastery as secondary stat
I enchant and gem with mastery (not to mention tanking oriented legendary metas and whatnot)
Sure I can swap to DPS and poke around with this kind of gear on me, but I would be very crippled. Mastery is the worst stat for DPS (and I'd want pure strength enchants and gems, not mastery). So with that in mind I still need 2 sets of gear and I don't see how that would change in WoD, it just smooths out the swap a little if you're missing a few pieces for your offspec.
Do tell me if I'm missing something