Healing plate. In a typical group, when it drops, everyone gives a collective grown and the seemingly endless amount of ret pallies roll for it on their offset. Yes, I'm exaggerating (Not by much, though, just a few weeks ago I ran a VoA10 with 4 ret pallies DPS, and 1 paladin tank), but still, the problem remains.
Spellpower plate is on one end of the spectrum of number of usable specs vs. the number of specs that primarily use the armor class.
What that means, in readable English, is that out of the 7 possible roles that use plate (2-Tanking and DPS for Warrs, 2-Tanking and DPS for Death Knights, and 3-Tanking, DPS, and Healing for Paladins), only 1 possible spec, the holy paladin, can use it.
Compare this, for example, to +agility leather, out of the 5 different roles played by leather wearers (Ranged DPS, Healing, Melee DPS, and Tanking), 2 of those use it. That's 40% compared to 14%
Thus, we get into a situation where if a +agility leather piece drops, and it get sharded because you don't have a feral druid or rogue in the group, it's a shame, whereas when the same happens to spellpower plate, it's "BLIZZARD SUX AT ITEMIZATION!"
The most predominant suggestion to fix this is by making holy pallies use +strength plate. That would lead to either talents or masteries converting strength int spellpower, agility into spirit, and so on and so forth. That is an inelegant and cumbersome solution by any measure, and if you thought protheal paladins were bad in arena, wait until you get paladins that hits and bursts like a ret pally, and specs holy so that it heals like a holy pally. It would be a nightmare to balance.
I believe that there's a better way, and it involves DKs in spellpower gear.
No, I assure you, I'm not that terrible of a DK. By making DK DPS use spellpower plate, it evens out the gear to role ratio: from 1/7 to 2/7. It may not think like much, but think how many Death Knights are in your raids right now, they'll soak up the spellpower plate like candy.
I can feel every single holy paladin twitch in apoplectic rage at DKs stealing their loot, but let me explain. Look at how much plate DPS items drop, especially compared to spellpower plate. This will allow Blizzard to even this out by dropping more spellpower plate. Sure, DKs will be fighting you for gear now, but there will be more gear to fight over to offset the problem.
Another plus side is that this is all reconcilable to lore, thanks to the large number of spells that Death Knights cast. If you'll remember, death coil is just as much a warlock spell as it is a death knight spell. Plus, with many Death Knights just being fallen paladins, it seems reasonable enough that they would keep the same gear, as well.
Now, too, DPS warriors and ret pallies will be happy, as they would no longer have to fight with DKs for gear.
The one problem I can see with this is weapons. Currently, Death Knight weapons are all melee stats, and unless we want to completely take out death knight 2-hander DPS and have them dual wield spellpower weapons, there's nothing currently available to make death knight weapons under the new system. Plus, where does that leave tanking Death Knights? (I'm not including tanking death knights in this proposed system to avoid cases where someone can spend their 76 points into a tree and get all the tanking and DPS talents, and wearing the same gear, be both unkillable and do great damage. There's just no getting around tank gear)
The best I've come up with is to drop +spellpower 2 handed weapons, and make holy paladins as well as DKs use those, but that introduces more clutter in loot tables and doesn't solve Death Knight tank problems.
Though, with that, perhaps one could put in a talent or mastery that change spellpower stats to an equivalent tanking stat, and since DK DPS and tanking were designed to use the same weapons anyway, wouldn't cause protheal problems to nearly as much of an extent. However, that seems like an incredibly ham-fisted and inelegant solution.
The same concerns apply to reforging, as well, they are designed, from what it looks like, to be slight stat changes, not complete stat overhauls, and it would again be a cheap and inelegant idea to force tanking DKs to use reforging.
Looks like I'll have to ponder this some more, until next time...
...I need a catchphrase.