AHA! So I was right about them being ahead of schedule! That means Hero and Banjo are, for the most part, done, and probably just need testing and finishing touches. This means character 4 may well be in development along with character 5... and who knows what else. They started on Joker in December (late November, more like?), and we're in July, which is the halfway point (to February, the cutoff date). Halfway through this, they finished Plant, Joker, and the bulk of the DQ heroes and Banjo.
It sounds to me like they're just spacing out reveals and releases to keep the hype train at a steady pace, but otherwise... the amount of headway they've made is extraordinary for the amount of time, especially considering how much has to go into the DQ heroes. I can only imagine 4 and 5 are in progress now by the core dev team, while a smaller amount of people are doing finishing touches (supervised by Sakurai) and preparing for bug-testing. If we can have four characters (about three and a half, more like, given Plant's state of nigh-completion in November) in seven months with only two remaining... that leaves a lot of dev time open. However, let's compare this to the fact that Sakurai said that the DLC team grows smaller as they complete DLC. It could easily mean those last two will take longer on account of that.
Whatever the case, it all sounds great... and it gives me hope for B-K to drop in late September or early October like I'm predicting. Gahhhh!!! I'm so excited!