Skill and class are more important than PvP stats. Much more.

Resilience rating can be checked fairly easily anyways.

With PvE, the dungeons don't change each time you go into it. So gearscore becomes a quick way of determining if your gear is appropriate for that particular content (optimally that's the intent, at least...let's please not start a "gearscore≠skill" argument here).

With PvP, you don't really need a quick way of determining gear. In a battleground, your best bet is having a team with a strategy and you probably don't have much choice in who you're grouped with. In arena...well, why wouldn't you have the time to just look at your prospective team member's armory to see what their gear looks like?

Besides...explaining your PvP gear is usually pretty easy anyway. "I'm full Furious/Relentless with X amount of resil."

GearScore is just as useful in PvP as it is in PvE. In both cases, it tells you if you have a high item level.

Well, think of being in a BG and instead of PvE GearScore showing up in the mouseover for your teammate, it shows PvP GearScore. I could mouseover the people around me and see "Whoa, this pally has a PvP GS of 5500+, I should stick with him!" or "This guy has a PvP GS of 3200, he's my cannon fodder"

Just look at the health bar, and the mana bar if they have one. That will give you a decent indication of where they are PvP-gearwise. I always shudder when everyone buffs up for AV and I'm still the only one in the group with more than 25k health...

Maybe what you'd like is an addon that shows you their resil next to their GS. This way you can find the guy with zero PvP gear.

You might be able to set up Pawn for PVP, although I'm not positive.