Bornakk's reply hints that Blizzard will probably just gloss over it as best they can -- they're not going to build a whole new 1-85 experience involving Deathwing. When you constantly update a five-year-old persistent world game like this with new stories and content, something's got to give somewhere. My guess is that Blizzard, being the perfectionists they are, will probably come up with a quest or two that gives a lore reason to go out there ("Hmm, you're too green to face the power of Deathwing, but our companions in Outland need help holding what's left of the Burning Legion at bay!"), and leave it at that. They may increase the XP and get you out of there even quicker, but going to Outland at 58 is still a gameplay necessity (Northrend shares the problem at 70, but of course we don't actually know what's going to happen with the Lich King quite yet). It's likely the lore will just have to deal.
World of Warcraft: Cataclysm will destroy Azeroth as we know it. Nothing will be the same. In WoW.com's Guide to Cataclysm you can find out everything you need to know about WoW's third expansion. From Goblins and Worgen to Mastery and Guild changes, it's all there for your cataclysmic enjoyment.