To be clear: Nothing is happening to Outlands or Northrend.
There are just some minor aesthetic changes. The Shattering/Cataclysm changes only affect the 1-60 Old World areas. The 60-70 (Outlands) and 70-80 (WOTLK) leveling zones are unchanged.
But, this just goes to show you the power of hype and how it shapes your perception. =]
Unfortunately, this hype can lead to false expectations and resulting disappointment. The new changes are pretty cool, especially starting in some of the Capital Cities. But, once you get over the initial novelty of the new cities and do some exploring - you'll realize that not a lot has changed in the 1-60 zones.If you've ever played "god games" before, you'll know what I mean. Everything looks pretty much the same, but it's like the developers just dropped in some trees and grass here-and-there, shoveled out some trenches, threw in some water, and reshaped some of the mountains. Once the geography was changed, it was just a matter of dropping in some new quest givers and NPCs.
For the new 80-85 leveling experience, don't set your expectations too high. I think the new zones are awesome, but please just ignore the hype as it will give you a false impression of what to expect. You might not remember this, but a lot of people complained about the new WOTLK leveling zones (ie, it was "too small"), but keep in mind that the new Cataclysm 80-85 zones are even smaller.
The original WoW had 2,600 quests (1-60), BC had 2,700 quests (60-70), WOTLK had 2,350 quests (70-80), and Cataclysm has just under 1,000 quests (80-85). (Note: 80-85 is supposed to take the same amount of time as 70-80 leveling.)
Although the number of quests isn't really a fair comparison of size, it does give you a pretty good idea of what to expect. =]
Cataclysm was more designed for the newbies and for veteran players who wanted to create new characters. It's a way to keep people playing longer, and encourages players to invite friends to play with them. Previously, many people didn't want to start playing WoW because of the sheer number of high-level characters and how far ahead everyone was - Cataclysm is a way to start players on an even ground and to bring in more new customers.
In regards to any New Realms, we won't know for sure until around Dec. 3-6. Currently, subscriptions counts don't warrant the creation of new realms and even with 1-2 million new players, it still wouldn't warrant new realms.
However, if Blizzard makes an announcement that "new realms are required to meet the demands of new players" - it sure would make their investors happy. =]
They might even wait until 1-2 months after launch to make it look like new realms were never actually planned and that they had to "suddenly" purchase and build out new servers and realms to meet the explosive growth. Realistically though, the new realms are probably ready right now and the servers were prepared months ago.