Even if he could say who the next singer is going to be, I think he wouldn't. They've been in this business a long time, they know that a little mystery can create a buzz. Buzz is good for publicity and record sales.
Think about it. If we all knew who the singer was this very instant, all the threads would be "This is Bullshit vs. I love it" or "I can't wait to buy the next cd vs. I'll never by another Anthrax cd in my life"
Hell, everyone is still debating John vs. Joey. (which is really fucking old now)