Beware: This pure speculation based on the current questlines, several level flow pictures and acknowledged cataclysm changes:

I structure the continents from north to south and west to east while I take a guess what questing will be about in Cataclysm:

Part 1 Kalimdor:

Teldrassil(green for minor changes): The taint in the new world tree might be more prominent but the night elves could be more interested in just containing the problems since it might be possible to restore the Old Tree now(It doesn't make sense that Malfurion returns to defend the Old World Tree, if it is destroyed for good). Another big objective might be building defenses against the Horde invasion.

Darkshore(red for extreme changes): Despite all the losses of territory to the south, the wreakage by the Cataclysm and the looming Horde threat, there might no longer be a problem with pollution from Felwood (more about that later) since the water on the screenshots is clean. So the questlines might almost exclusively focus on repelling the Horde and secure the torn lands.

Moonglade(green): Moonglade will be spared but extended with Shatterspear Village. The Cenarion might grow apart factionwise and Horde members could primary use Shatterspear now.

Felwood(yellow for moderate changes): I suppose Felwood will be cleaned from demonic corruption but aussaulted by Fire elementals of Ragnaros. I like my new name of Firewood The quests might deal with druids efforts to wipe out the last presence of the Shadow Council and to strike against the elemental invasion. Timbermaw Hold may have joined the Cenarion Circle.

Winterspring(green): There might be some fights with elementals but I believe that Winterspring will remain as it is because of its wild guardians - the moonkins. Perhaps the night elves will enforce their presence here.

Ashenvale(yellow): Heavy deforestation made by the Warsong clan and goblins. The night elves might be engaged in a covert war (Shadowmeld and the like) against the otherwise overwhelming invasion of Warsong troups. Perhaps there will be even low level pvp quests.

Azshara(red): As confirmed taken by the goblins but perhaps threatened by water elementals, some left over nagas and Alliance forces from Forest song. There might be a flight from the rising sea levels.

Stonetalon(yellow): Fights with fire elementals and interfaction wars. With the Alliance settlement at the peak destroyed the night elves might have errected a new settlement on the shore (I suggest you take the flight from Sun Rock Retreat to Zo'ramgar Outpost to get an idea which area I speak of) - this might be a the reason why there are night elven ships near the newly fortified Outpost in Ashenvale.

Northern Barrens(yellow): Crossroads might be a real fortress then and Northwatch Hold reinforced, Ratchet might be destroyed (the connection by boat redirected to Steamwheedle Port), the Harpies could be on the move(since they are nowhere else after the Charred Vale is almost likely a new staging ground for elemental invasions).

Durotar(yellow): The coastline might be swallowed by the sea, Nagas could appear, Sen'jin reconstructed into a Troll camp as big as Zabra'jin in Zangarmarsh and a bit more palms could emerge. Perhaps as a half floating village/port. Orgrimmar will be extended(perhaps it houses the port where Garrosh's invasion fleet started towards Northrend, a new entrance towards Azshara(confirmed) and new goblin quarters.

Desolace(yellow): Each side might now got two strongholds in the now verdant land but aside from the threat of the centaurs there will be a demonic invasion. The Kolkar are wiped out, the Magram have summoned the demons and be slain by them, the Gelkis and Mauradine allied against the factions and the demons. The satyr city is taken by the Alliance (The new settlement on the screenshots in my opinion).

Mulgore(green): Mulgore is closed to all outsiders but perhaps under attack off Theramore troops so the Tauren have given up every thought on peaceful coexistence and march to war to avoid being wiped out.

Southern Barrens(red): Palm forests, vulcanic rifts and the Alliance everywhere on the move. The Horde perhaps tries to raid the Alliance outposts in the region while the Alliance has to fight against the remaining quillboars.

Duswallow Marsh(green): The ogres are back near their old stronghold but almost certainly under heavy siege by the Alliance since Theramore is now on the move. Perhaps the Horde fights to secure Alcaz Island as a new stronghold and to evacuate their Ogres while the Alliance tries to take over the whole region.

Feralas(yellow): Since the salty plaines of Thousand Needles are flooded and the salty water flows now through Feralas, the once lush jungle is now a more barren landscape. Dire Maul might become a complete ogre related instance, Camp Taurajo and Thalanaar are destroyed in the progress of flooding. The new Tauren settlement is set atop the Twin Peaks in the north with an outpost new the ruins of their old settlement. The Ogres are on the move and both side struggle to keep them at the bay.

Thousand Needles(red): Brackish water dominates the region then and salt resistent plants settle the region. The old centaur caves are taken over by the Alliance and the great lift has been overtaken by them. The plains near Tanaris are a giant salt lake by then.

Tanaris: As mentioned before Steamwheedle Port is to be connected to Booty Bay, may got a flightpath and is a real port by then. The sand trolls might be on the move and try to resettle some of their ruins since the Silithid Hives are gone. To the south the Ogres have taken over the pass to Uldum and cooperate perhaps with the Twilight Hammer which transformed the former Hives in to cavern bases for the cult.

Un'Goro: The Twilight Hammer might plot to destroy the crystals and take over the region. Fire elementals appear more often and the Silithid Hive has been extended.

Silithus: The war with the Twilight Hammer and the last surving Hives goes on with new efforts.

Thus far Kalimdor, I try the Eastern Kingdoms next week. I hope I have reasoned enough so that my speculations are at least plausible. Other thoughts are welcome of course.