Like Gaige, it will be a standalone release.
Since it was a new character, like Gaige, and Gearbox was already working on raising the level cap for the game – along with news that it was taking longer than expected due to the amount of work to be done – many started to suspect that maybe the sixth Vault Hunter would be included with the level cap raise update.
CEO Randy Pitchford recently clarified this, when a fan asked if the new character would be a standalone update like Gaige. Pitchford simply responded with “Yes”.
— Randy Pitchford (@DuvalMagic) March 10, 2013
So while we’re not sure when we’ll see the new character or the level cap raise update, we at least know that they’re two separate entities. Which now makes two DLC pieces that Gearbox has unreleased rather than one.