Mangini's damn cool - stellar drummer, in fact - but he doesn't have the same force of personality as, say, Minnemann or Macaluso or Zeleny or especially Lang.
He'd not be my favourite choice, seems a little too obvious and safe. I'm quite looking forwards to going "Ooh, I wonder how THAT'll sound," whereas I think Mangini Theater would be a little too far along the lines of "business as usual." He's not a Derek or a Jordan, where you hear all those rock and roll patches, or the mad spidery technical stuff. If anything, Mangini's slightly more reserved than Portnoy.
That said! The fact that it'd be "business as usual" gives it a great deal of weight. No idea how reliable the sources are, and I'll look forward to Mangini Theater should they be correct. But not as much as I'd be anticipating Minnemann or Macaluso Theater. I like the idea of this mad, brave new world. I think Mangini's probably a bit too sensible a successor for my liking.