An earlier interview implied that characters take almost a year to develop, so if paid DLC appears in less than six months, I'll be mildly disappointed about the apparent mistruths going on in these interviews. Of course, I'll still buy it assuming it's not a total rip-off, but that's beside the point.
Well, Mewtwo is planned for spring, which is about six months from now and he's probably all we'll get then. Maybe next summer or fall we'll get more DLC. But, if we do get some more playable characters in DLC within six months, it might not be a mistruth.
There are probably other characters that they worked on that ended up getting scrapped (such as what usually happens), but now, thanks to DLC, they'll be able to complete them and release them. So they may not have to start from scratch when it comes to making newcomers for DLC. I assume this was also the case with Mewtwo, but Mewtwo is farther along than any other character as he was a higher priority.