The Beginning
Everything begun around April 2007 when some job ads showed up on Blizzard's careers site seeking developers for a Next-Gen MMO.
Not a WoW Expansion
On the end of 2007 Drysc announced that the Next-Gen MMO mentioned on job ads won't be an expansion for World of Warcraft.
Drysc's quote: (Source)
No, it is an unannounced Next-Gen MMO.
And that doesn't mean an expansion for World of Warcraft either.
Brand new IP
Blizzard's poster Zarhym confirmed that the Next-Gen MMO will be based on a brand new Intellectual Property (IP), so no Diablo or Starcraft MMO. For some time it was rumored that it would be a Call of Duty MMO since Blizzard merged with Activision, but since Zarhym official said it would be a brand new franchise, new art and new lore, CoD MMO is off the case.
Ensemble & Halo MMOZarhym's quote: (Source)
We have nothing to advertise for the new MMO because it's a shell of a game thus far. We've already stated it'll be a brand new franchise, which means the lore, art, and game play are being developed entirely from scratch. It's an overwhelming process, but a process through which we excel. Our track record supports this.
After the leak of Titan, it was found that the same name was used for Ensemble's cancelled Halo MMO - Titan MMO. Also several people from Ensemble Studios were hired from Blizzard after Ensemble was disbanded on 2009. While, people believe (hope) for a Titan being the Halo MMO, it is almost impossible that this is the case.
Broader Audience
The following part is a bit unclear, please check and tidy up.
Bobby Kotick said on Deutsche Bank Securities Technology Conference, that the Next Gen MMO will target a broader audience.
Bobby Kotick's quote: (Source)
What we've announced at Blizzard is that we have Starcraft [II] coming, Diablo has been in production...and a new, unannounced MMOG that has a little more broad appeal
Sci Fi / Fantasy
In the past Kaplan, who revealed that he is involved in the project, was asked if the game's genre would be science fiction, post-apocalyptic, or historical, and while laughing he responded: "all of those combined!".
Also, according to some job listings and some inside sources the game will be a Sci Fi/fantasy MMO.
Blizzard's quote:
2+ years game development experience modeling and texturing sci-fi and fantasy character armor and weapons for next-gen art pipelines
MMOFPS & Social Aspects
Main article: Leaks
A French gaming site reported that according to some anonymous source the game will be a MMOFPS (Massively Multiplayer Online First Person Shooter) with several social aspects offering the player two "sides"; the combat side and the social side of the game.
Titan
Main article: Titan
Project Titan was firstly mentioned on various forums during 2009 but was treated as yet another rumour. Only on December 11, 2010 at SpikeTV's VGAs, Frank Pearce was the first Blizzard official to confirm Titan as their "next gen MMO" .
Auf MMO-Champion gab es vor kurzem jemand der sich die derzeitigen Entwickler von Titan mal genauer angeschaut hat und zwar ihr Portfolio.
Wenn man die Bilder mal genauer betrachtet fällt auf, das die Charactere sich irgendwie ziemlich ähnlich sehen obwohl es von sie von mehreren Entwicklern sind:
Image from Joshua Singh's Blog:
Images from Renaud Galand Gallery:
Images from Marc Brunet's Gallery:
und wenn man dann noch an das hier denkt:
Sci Fi / Fantasy
In the past Kaplan, who revealed that he is involved in the project, was asked if the game's genre would be science fiction, post-apocalyptic, or historical, and while laughing he responded: "all of those combined!".
Also, according to some job listings and some inside sources the game will be a Sci Fi/fantasy MMO.
Blizzard's quote:
2+ years game development experience modeling and texturing sci-fi and fantasy character armor and weapons for next-gen art pipelines
sieht das ganze garnichtmehr sooo abwegig aus