My opinion is spell/dot cleave will reign, but what classes exactly?
I was Disci in RBGs and almost 2k (I know that not so much) for whole Cata so I start from healer choices. My choices are:
Holy Paladin - best healer for Cata, solid Tank healing, strong AoE healing, seems that nothing will change here
Resto Druid - big come back in MoP. Best AoE healer in game; buffed survivability in MoP. Absolutely my choice
Rest Shaman - Cata was a roller coaster for rshamans, but they always we're able to be at top RBG healing done. They were losing spot because HPalas were doing even better but with HC DoT Cleaves their abilities and passive healing proved to be better. They were losing spots to Disci because of only one spell - Mass Dispell that is on 15s cd in MoP - seems to long for Disci to be considered here so my last opt for healer is shaman.
Damage Dealers in MoP - we already know that some classes like Mages are beyond everything. Fire is absurd while Frost is not better. Everyone complains about Shadow Priests and additionally they have Mass Dispel which is supreme. Affi Locks and Boomkins have some synergy with Fire Mages and Shadow Priest and Destro Locks can burst people in two globals now. Frost DKs were best choice for target callers but were unneed while dotcleaves were superior but on the other hand the're AoE DPS class so they fits well in DoT cleave idea. Lastly Arms Warriors, Assa Rogues and BM Hunters are by far strong. IMO I can;t judge what setup will be best but choices should be take from this who I mention.
At the end there are two questions. How are Druid Tanks compared to Prot Wariors and the biggest one - how will Monks be.
P.S. Well, maybe I can't deny - dot cleave wont be supreme and burst setup with shadow, ele, arms, assassination, beast master and frost DK will be just best.