"First, it's a conversion nightmare. Strength would have to do nothing for them. You'd have to convert hit into spirit and expertise into . . . well, that would be the conundrum, wouldn't it?"

Why worry about what str will do for them? The strength is turned into Intellect. They don't get both. Hit into spirit could work. There are already classes that do it the other way. Why does expertise have to turn into anything? It's not on every piece of plate gear. If a piece has expertise then clearly it's meant for a melee.

"Second, it ignores the other slots. Do Holy pallies use Str-based two-handers? Spell weapon and shield? What about rings, necks, and trinkets? If they could double-dip like that, it means that you'd now have holy pallies legitimately rolling on more gear than before, which just exchanges the previous problem for a different one.

Why would you take a 2h weapon to get 300 intellect from the strength instead of a 1h weapon that gives you int and over 2000 spell power? Using a 2h weapon also stops you from using a caster off hand or shield.

If they want rings and neck to be melee specific, then put expertise on them. Most trinkets have some kind of one use affect or a proc that are usually very specific to either casters or melee so that's not a problem either.

"the only imbalance i see is the ease of gearing up 2 specs with 1 armor set having 1 set for both ret & holy that is"

Like resto/ele shamans, boomkin/resto druids, and priests almost already do? And just like those specs, you're not going to wear the exact same gear. You'll still swap out some if not all trinkets, weapons, and jewelry.