Randy Pitchford has been very vocal about Borderlands 2 all throughout its development. The president of Gearbox is even nice enough to answer questions via Twitter, even going as far as revealing some spoilers about upcoming DLC, which will include a level-cap increase and a new character class.
The Examiner was dedicated enough to spot the tweets on Randy Pitchford's account, which means they're either really into Borderlands 2 or they have a secret dev-crush on Pitchford and like spying on his Twitter in the wee hours of the night. I'm going to go with the second one because it seems more plausible. Anyway, Pitchford was asked about new character classes via DLC, to which Pitchford tweets “yes - we're working on it.”
Pitchford is also drilled on a level-cap increase, where a user asks if there will be an increase to which he simply replies with “Yes”. Regarding the banking system and backpack upgrade, Pitchford says “that's being talked about. Not as simple as it sounds...”. It would have seemed like the banking system from the first Borderlands should have carried over to the second Borderlands, but why add necessary features for free when you can charge $4.99 for something everyone will want?
The most interesting question was about Eridium, the game's rare-as-a-virgin-in-Las-Vegas resource that can be used for a few not-so-necessary purposes in the second game. The user comments that it doesn't seem like it's worth picking up, and Pitchford retorts with “We've got plans for this brewing..”
Ohh, plans brewing? That sounds legit.
Pitchford doesn't give a timeframe on the content but given that they can churn out new DLC pretty quickly, there's really no limits as to how much content they can add to Borderlands 2. In fact, the only limit will be your hard drive space.