-What if Cataclysm was longer than your average expansion?
-What if Cataclysm was broken in to many little patches like Vanilla?
-What if the actual Cataclysm didn't happen right with the launch of the expansion and instead the revamp happened in a later major patch?
-What if the main cinematic of Cataclysm showed N'zoth's slimy tentacles getting everywhere?
-What if the Cata launch showed Twilight's Hammer cultist's infiltrating major cities? What if players could join them and wreak havoc?
-What if Cataclysm went from level 81-90 with the same zones?
-What if level 90 unlocked Path of the Titans as a new talent tree system specifically for max levels?
-What if the launch content only included Bastion of Twilight, heroics, as well as Scenarios?
-What if Goblin was the only new race with different Cartels going with Horde or Alliance
-What if Goblins and Gnomes began teaching their main craft: Tinkering, as a class?
-What if heroics were kept easy, but challenge modes had been added at the start?
-What if the WotLK model of raiding had continued and we had no need for LFR?
-What if the first major patch had a revamp of SMV/Outland as Netherdrakes flooded through the Dark Portal followed by Sitheria as well as Heroics and a questing area added/updated to Blasted Lands?
-What if the second patch ended with the rise of Deathwing Cinematic with the Cataclysm?
-What if the third patch saw Deathwing and Sitheria ressurecting their children and with it the Blackwing Descent (Sitheria moved here) and the rebuilding of the destroyed Azeroth (revamp)?
-What if the fourth patch saw daily areas open up in the Chasm in Vash'jir, the floating Islands in Uldum and the Firelands in Hyjal?
-What if, a month or so later in a fifth patch, the Elemental Lords rose up and we had a single tier with 3 raids for Neptulon, Ragnaros and Al'akir?
-What if the sixth patch brought the perpetrator N'zoth to light with 5 mans in CoT?
-What if the seventh patch brought back Azshara and with it Tidal Waves submerging most of Azeroth?
-What if the eighth patch dealt with retrieving the Dragon Soul put in the charge of the Dragon Aspects instead of Thrall?
-What if the next 3 patches dealt with staging an assault on Azshara and then Deathwing?
-What if the final patch finally brought N'zoth to the forefront and with it the defeat of the Heroes of Azeroth
-What if a final "mini-patch" showed Kil'jaeden stepping through the dark portal and N'zoth stopping his onslaught to meet his new foe in battle?
-What if Blizzard delivered on the promises between WotLK and Cataclysm for PvP?
-What if burst really did get reduced?
-What if CC didn't see an exponential increase?
-What if Tol Barad was never added?
-What if Wintergrasp was updated with Cataclysm launch and wrapping up of the WotLK story?
-What if AV was moved into the game world and returned to it's original glory?
TL;DR There's 2 main points here: Cataclysm could have been so much more and so amazing. But most importantly, Blizzard could easily allot resources to follow a Vanilla level patching cycle with little but major patches in between. Blizzard could also continue an expansion for even up to 3 or 4 years in order to make sure that they could tell the stories they want to and leave nothing out.