The 15" PowerBook is sticking around so that Mac OS 9 users can buy a new Mac to do whatever they need to do that OS X isn't yet capable of.
I'm going to throw my hat in the "iMac gets a 970" ring, which is a bit of a change from the position I've taken before. First of all, remember how Steve introduced the iMac? He emphasized the fact that it was not last year's technology. Well, after the pro line goes 970, the G4 will be last year's technology. If the iMac continues to more-or-less follow the PowerBook, then I expect it to sport a 970 late this fall, or perhaps at MWSF. Both can use the lower-voltage (and thus, lower wattage and slower clocked) 970s, leaving the PowerMacs to keep the highest MHz rating (in addition to whatever other enhancements Apple decides to throw into their workstation line).
I don't think either of the boards that MacWhispers is talking about is an iMac board, or a PowerBook board. Not yet. I don't think it's a PowerMac board either.
There seems to be some controversy over whether Panther is sufficient to reschedule WWDC, or if the 970 must be involved as well. I think the first is closer, but both alternatives miss the point. First: As Programmer
and others have pointed out, very little will need to be done in order to move from the G4 to the 970, all else being equal. Most programs won't even need a recompile, because the 970 already supports PPC and VMX, and most programs can live happily within 2GB of virtual memory. Faster performance will come automatically and transparently. So the 970, in and of itself, is no reason to postpone a developer conference. I think Apple is right: Panther is
the big news. But why?
Well, think about it: An operating system's job is to exploit the hardware; more precisely, to package the capabilities of the hardware into a developer-and user-friendly form. Apple has gotten really good at making sure that OS X uses the available hardware efficiently (QE being one example). So, if all the hardware is going to be is 970-based PowerMacs that are as close to the older variety as is practical, and which are intended to be used in much the same way, then there's really nothing new or radical for the OS to do. Panther would be more evolutionary than revolutionary. But if the hardware were capable of behaving in altogether new (to PCs) ways, and Panther exposed, say, pervasive Rendezvous enabled distributed computing, assisted by Cocoa's existing ability to disguise a remote process as just another task running next door, and if it was implemented as core functionality, then Apple would be introducing a new (again, to PCs) paradigm, and they'd be deeply interested in getting as many of their developers on board as possible.
Food for thought.