Actually, Blizzard has worked on improving the lore point of view in WoW recently. Take the Sunwell thing for example. They've brought this culmination, so to say, to the entire TBC story and its series of betrayals. As far as the lore's concerned in WotLK, they've made progress so far, moving Garrosh Hellscream to Northrend as a new leader and probably a successor of Thrall and all.
So I think wc4 should cover a story continuing after the culminations of TBC and WotLK, but simply condoning the defeat of Ragnaros, C'thun and all the dragons and such, as minor battles.
Perhaps the story of wc4 could revolve around the war between the Legion and the newly formed "Army of the Light", which the Naaru predicted would be created by the dreanei and the Alliance. The high elven order could be restored by those who survived the cataclysmic tragedy of the blood elves. Argus, the legendary homeworld of the Eredar could be a new location to be fought over. Sargares, could re-materialize and take charge of things once more. The Forsaken could rise to power in Northrend and pose a new threat to Azeroth. You name it...
