While it has not been officially announced yet, with warrior sunder armor now offering 20% total armor at 5 stacks about wow gold, one can only expect expose armor to get the same treatment. I was all for expose armor being a percentage based ability the one patch we had it at 30% (45% when fully talented) back in classic before they pulled cheap wow gold. It is 4000 armor on a 20000 armor target, which is almost exactly the same as the expose armor of today. Against cloth, leather, mail, it is worthless.

What If You Spec/Gear Around It?

-20% Expose Armor

-10% Mace Spec (I assume this will be 10% armor, 5% haste)

-5% Serrated Blade

+10% haste from lightning reflex

With 3 red, 3 yellow and 3 blue gems (using +27 armor penetration rating gems for blue sockets), you can have roughly 150 more armor penetration ratings, or 10% more armor reduction and 7.5% more haste assuming they merge armor penetration rating with haste rating. -30% armor and +20% haste passive? That will make a significant difference, even in PVP. Rogue/shaman synergy should even be better as with blade flurry, slice and dice, windfury totem and heroism, you can put amazing pressure on your target for wow gold.