It seems to me that it is more likely that we'll be seeing Merom based PBs in the second half of '06 as the first IntelBooks.
I seem to recall Jobs saying two things:
"I think a lot of you would like a G5 in your PowerBook and we haven't been able to deliver that to you yet."
"So when we meet here again this next time next year, our plan is to be shipping Macs with Intel processors by then, and when we meet here again two years from now, our plan is that transition will be mostly complete."
Now, his "plan to be shipping" IntelMacs by June 2006 seems a somewhat reserved for Jobs if his intention is to be releasing new Intel-based products 6 months before that. This seems to imply that Q2, or thereabouts, is their target for whatever they release first.
I'd imagine that a mini would be the easiest product to redesign, its FF would likely remain identical, with only its MOBO and some internal components changing. A PB would be much more difficult, and I really don't think there is a chance in hell they could design and have the capacity ready to ship an ENTIRELY new PB in six months.
Also, Apple will obviously want to be all over the Merom when it comes out. They have been hyping 64-bit for ages and when the Windows world starts going that way (Vista), they are gonna have to be right there. I don't know the design considerations (electrical, software, physical...spiritual) when moving from the the Yonah to the Merom, but I don't imagine it's trivial.
Not to mention (although it already has been) that if Apple releases the 32-bit Yonah in the interim, they are left supporting an architecture that will only exist for 9-10 (?) months for the next 5 years. That doesn't make much sense.
If the redesign for Merom is considerable (and I don't know if it is) I don't think we are going to see Yonah-based books because you know Apple is going to want to be right there when the Merom is available.
If the design/engineering work for a 970FX is far enough along (we all know this is some cud Apple has been chewing on for more than a year) then we might see a PowerBook G5. It would sell like crazy, and that's always nice.
It's probably more likely, however, that Apple is going to use a G4 update to hold the line together for the next year (one update in between now and late 2006 is entirely reasonable given the recent revision cycle) be it the 7448, 8641, or whatever. It's a safer and easier solution that, unless they are REALLY far down the G5 road, makes the most sense given every consideration.