He didn't specify whether he meant additional outside characters in Street Fighter X Tekken or more crossover games. But he did suggest that more collaboration between Namco and Capcom was in the offing, beyond the two announced Street Fighter/Tekken crossovers. "We have these two giant companies, Capcom and Namco, working together. It would be kind of wasteful to limit it to just Street Fighter and just Tekken, and that's all I'll say."
This is just speculation, but we wouldn't be surprised to see some Soulcalibur V characters in SF X Tekken, at least. It would be effective cross-promotion. And X-promotion.