I can almost guarantee that some "power-" machine will be white. PowerBook, PowerMac... something. All I know is that they'll definitely do white on some new product, because it fits with all their existing looks. Then there will probably be a very new look for the PowerBook after that. But come on, a Titanium tower? It would look like a 1950s refrigerator!
Apple may do something vaguely "Ti-esque" but I don't think it's all that likely. Notice the old PowerBook's black never made it to any other machine. I doubt the Titanium look will either. (No, the QuickSilvers do not count.) Frankly, I'm getting tired of the Titanium look, because next to the new iBook it's so boring-looking now. Steve is probably thinking the same thing. Speaking of Quicksilvers though, why not a Quicksilver-inspired PowerBook? Not quite Titanium, but sort of midway between Ti and Silver... it could happen.
On the other hand, what about a black desktop tower? Like, a good black, not Dell's patented CrappyBlack™ . What do you think? Looking vaguely Pismo-esque? I think it's possible... but I do think white is in first.