In the latest alpha patch, WoW introduced a new gearing mechanic: Secondary Stat Attunement. Each specialization is "attuned" to a specific secondary stat, gaining 5% more of that stat.
I am doubtful that this will be a good idea.
First off, I'm not entirely certain what advantage this mechanic brings. It might spread out the secondary stats, so that different specs chase different stats and thus chase different gear. It is a bad situation if the same piece of gear is Best-in-Slot for every single class.
It may also help a new player who doesn't know which secondary stat to look for. If they at least make sure that they have their attuned stat, it gives them a small basis on which to compare gear.
The problem, though, will come if the attuned stat does not match the theorycraft. Essentially, the theorycrafters will end up ranking the secondary stats for each spec. Gear with the top two secondary stats will be Best-in-Slot. If the attuned stat is one of those top stats (preferably the top one), then things will work out.
However, if the attuned stat is 3rd or lower on the ranking, Secondary Stat Attunement turns into a massive trap for the new player. The heuristic, "My Attunement is Critical Strike, so I should look for Critical Strike gear", is not just wrong, but it will cause new players to discard better gear in favour of worse gear. The potential for misleading people seems very high. Not to mention that it might cause loot arguments where players insist that specs must take gear with an attuned stat.
As well, it does seem like the possibility of multiple builds will be lessened. Arguably the most interesting time to be a Holy Paladin was back in Cataclysm when we had the Mastery builds and the Spirit/Haste builds. Having an attuned stat seems like it will always push us towards one specific build.
A specific problem with Holy Paladins is that the current Attuned Stat is Critical Strike. It's a nod to Vanilla and TBC when we desired Critical Strike above everything else.
However, healers are generally not fond of Critical Strike, no matter what the math says. Critical Strike is unreliable in the short run, and healing is all about the short run. Back in the day we chased Crit because of Illumination and mana regen, and mana regen belongs to the long run, when the Law of Large Numbers kicks in. As a means to recover mana, Critical Strike was great. As an aid to healing, it's suspicious.
Healers far prefer stats which always work. Sometimes healing pushes you to be pessimistic. In the crunch, Critical Strike will let you down.
Now, if heals are much smaller than health pools, then it's not as bad. As well, it does synergize well with Mastery, so if Mastery is our other chase stat, then it will work out decently.
The probability of Secondary Stat Attunement going badly and causing issues is high. High enough that I think it outweighs the potential benefits. The game has been fine when letting the theorycrafters determine the best stats from the basic math. Forcing the different specializations to have different "best stats" through this mechanism is overly heavy-handed, and likely to backfire, in my opinion.