I think by fighting characters, I think he's talking along the lines of characters like Ryu, Heihachi, and Akira. He wants to avoid adding generic fighting game characters in that kind of way, and if you're familiar with fighting games of that light, you can see why it would be discouraged. This doesn't mean that characters that have appeared in a fighting game won't happen, because we already have several characters like that already. It's simply a way to promote and encourage diversity, so please don't look deeply into it.