I would imagine that the DLC will be released sooner than we actually think it'll be. Remember, when they first announced the two new characters, they hadn't even started working on them at all yet. And now we already have full fledged videos of them fighting, along with some screen shots. So to me, sometime in January sounds absolutely reasonable at the given pace the SuperBot is working at.
I would hope soon, it's been out nearly 2 months, so we're close to that 'first DLC window' I would think, 3 months for each batch of 2 characters (assuming there'll be more) would be a bit rough for me, 2 months apart feels more comfortable. So here's to hoping we get some sort of announcement real soon!
I would just like to say that there doesn't need to be a "HERE COMES A NEW CHALLENGER!" videos for them.
They can release the videos latter if they made them.