So far this is what I've seen for compositions from EU and US at 2200 or above (or seen on stream over 2300 mmr) so far.
By class/spec (only listing DPS, if you are a healer you can basically replace almost any healer in any comp with some exceptions)
Deathknight
DK/Hunter/Hpal
Dk/Warrior/Hpal
Dk/Lock/Shaman
Dk/Rogue/Shaman
Dk/Feral/Hpal
Dk/Spriest/Shaman
Dk/Monk/Hpal
Dk/Double healer
Dk/Enhance/Hpal
Dk/Ret/Priest
Warrior
Warrior/Hunter/Hpal
Warrior/Double healer
Warrior/Mage/Druid
Warrior/Lock/Shaman
Warrior/Spriest/Shaman
Warrior/Ret/Priest
Warrior/Feral/Hpal
Warrior/DK/Hpal
Warrior/Warrior/Hpal
Warrior/Enhance/Hpal
Warrior/Monk/Hpal
Hunter
Hunter/Rogue/Priest
Hunter/Enhance/Druid
Hunter/Warrior/Hpal
Hunter/Hunter/Hpal
Hunter/feral/Priest
Hunter/DK/Hpal
Hunter/Monk/Hpal
Hunter/Spriest/Shaman
Hunter/Ret/Priest
Ret paladin
Ret/dk/priest
Ret/Feral/Disc
Ret/Enhance/Druid
Ret/Warrior/Priest
Ret/Hunter/Priest
Ret/Ele/Priest
Ret/Spriest/Shaman
Mage
Mage/lock/shaman
Mage/mage/shaman
Mage/rogue/Priest
Mage/spriest/druid
Mage/Feral/Priest
Mage/Warrior/Druid (shaman variant at 2700)
Mage/Elemental/Priest
Mage/Boomkin/Priest
Spriest
Spriest/monk/shaman
Spriest/lock/shaman
Spriest/Mage/Druid
Spriest/Rogue/Shaman
Spriest/Warrior/Shaman
Spriest/Ret/Shaman
Spriest/Feral/Shaman
Spriest/Dk/Shaman
Rogue
Rogue/Lock/Shaman
Rogue/Hunter/Priest
Rogue/Dk/Shaman
Rogue/spriest/Shaman
Rogue/Mage/Priest
Rogue/Rogue/Priest
Rogue/WW/Priest
Rogue/Boomkin/Priest
Lock
Lock/Warrior/Shaman
Lock/Spriest/Shaman
Lock/Rogue/Shaman
Lock/Mage/Shaman
Lock/Monk/Shaman
Lock/Dk/Shaman
Lock/Feral/Shaman
Lock/Enh/Druid
Enhance Shaman
Enh/Warrior/Hpal
Enh/Hunter/Druid
Enh/Ret/Priest
Enh/Dk/Hpal
Enh/Lock/Druid
Ele Shaman
Ele/Mage/Priest
Ele/Ret/Priest
Ele/Rogue/Priest
WW monk
Monk/Spriest/Shaman
Monk/Lock/Shaman
Monk/DK/Hpal
Monk/Warrior/Hpal (this got r1 last season with chardex on monk)
Monk/Hunter/Hpal
Monk/Rogue/Priest
Monk/Feral/Hpal
Feral Druid
Feral/Warrior/Hpal
Feral/Mage/Priest
Feral/Spriest/Shaman
Feral/Lock/Shaman
Feral/Monk/Hpal
Feral/dk/Hpal
Feral/Hunter/Hpal
Boomkin
Boomkin/Rogue/Priest
Boomkin/Mage/Priest
By far the least represented are boomkin and ele (both which people think may be strong this upcoming season)
BUT by far the most different compositions i've seen played in a long time.
Have a fun season guys.