I'm an everything guy - arena, rbgs, random bgs, world pvp, and pve. I think shaman look viable for all. Viable for 2200+ arena? Only time and experience at 90 will tell. But I don't think 1800 will be hard at all and maybe 2000 if you put the time in. That'll give you the increased points cap to get geared up and blow things up in other types of PVP where I think shaman can really shine.

Although shaman have some very promising talents with the dynamics to potentially hit very high rating arena, other classes have a lot of things that could give us trouble that we'd have to overcome, or if not, just get hard countered and blown up to melee cleaves like in wrath.

I'm not interested in banging away at 5v5 for an entire expansion trying to earn a minor tier 2 upgrade, and even less so - titles. If I really get into arena I'll play solo or dual box 3v3s or something.

I only went to 2000 in 5v5 in wrath to get fully geared when there were rating requirements, by 2100 it was no longer fun - but with that gear all other pvp was amazing. I focused on BGs and Wintergrasp at that point, and heroic instances. For the latter, LFR gives us a way to get excellent gear compared to being stuck 2 tiers behind from the justice vendors.

I didn't box in Cata but based on what I observed, Shaman were good but not amazing in non-arena settings. I think with increased burst capability with ascendance and the like, coupled with the ability to spec all survivability and healing (with the super OP healing tide totem), you can be a powerful force in BGs and world pvp without quickly getting mowed down when the fight gets to more than 4 people, or 2-3 skilled players aoe cc'ing you down and outhealing your burst.