Here's my say...
Either their going to up the XP rate per kill/quest or no new expansion. 70s in BC* had about the same number of zones that Wotlk does for 80s, but they also had to up the xp rates so that becoming 80 wasn't insanely lengthy and depressing... I believe that they added the random Dungeons and BC que thing, so that players who did BGs, and who like to dungeon level can gain xp just as fast.
If another expansion does come out after Cata, it's probably going to either...
A) Increase the XP rates dramatically
B) Find some other way to balance the XP gain where it doesn't take so long
C) Give up and say.. screw it, they can spend all year on leveling through this shit see if I care!
I honestly think they won't add another Leveling expansion though, seeing as they had to make the next level cap 85 so they wouldn't have to alter the rates too much, or not at all, and also because they didn't have alot of land left to work with. They are trying to somewhat stick to the lore, and base continents off of continents that they already created in the Warcraft books. Adding more continents would really upset alot of lore fans that play wow just for the fun of questing and following the story.
It is possible though that they might use the already existing Emerald Dream for next expansion?
I think that would be a great idea, and honestly thought that the expansion after Vanilla was going to be emerald dream, but never happened. So many players love the mystery in WoW, and how it started. Emerald dream would make so much sense, considering they are adding Hyjal to cata, with the tree of life, which gives a very good indication that Emerald Dream is coming.
Either that... or they are going to use Norse Mythology to make their next expansion. Why norse mythology? I've done some research on wow, comparing things and such, and noticed that alot of their stories comes from the stories of Norse Mythology. Here is a small list comparing creatures and legends in WoW, with those of Norse mythology.
Norse Mythology Names - WoW Names
Surt - Ragnaros
Loki - Loken
Thor - Thorim
Fenrir -
Havn't found yet
Jormungand - Jormungar
Skadi - Skadi
Skoll - Skoll
Hati -
Havn't found yet
Freyr - Fraya
Odin - Hodir
Mimir - Mimir
Garm - Magmadar
Hymir -
Havn't found yet
Heimdall - Malfurion
Tyr -
Havn't found yet
Vidar -
Havn't found yet
There is a part in Norse Mythology in which Surt the Fire God (Ragnaros) tries to destroy the World Tree (the big tree in the NE section of Hyjal), Yggdrasil (funny how Teldrassil is a Night Elf zone in WoW, and how Malfurion the night elf guards the world tree) and the proud defender Heimdall (Malfurion) signs his horn to call for the titans to stop Surt.
The event of which Surt destroys the world tree is called Ragnarok. Ironic right?
There are alot more little connections that I won't go too into detail about, but supposedly after Surt destroys the world tree, he sends a fiery reign across the world, which after 100 year is recreated with beautiful life, and Is home to giants and humans. Wonder if blizzard will take a similar approach, seeing as Ragnaros is taking a big part in this next expansion, and the Plains of Elements.
Thanks for taking the time to read all this
~Vortalex