There are four kind of chips Intel is offering for laptops: Celeron M, Pentium M, Core Solo, and Core Duo.
Pentium M has just been made obsolete by Core Duo, which is faster at the same price. Celeron M is cheap, and almost as good as Core Solo. Core Duo is only a tiny bit more expensive than Core Solo, at twice the performance. That is why I don't think there is any chance of a Core Solo; it is the wrong chip if you want a cheap chip, and it is the wrong chip if you want performance.
With today's announcement, it might be just about possible that Apple will ship iBooks with the slowest Core Duo, because they will want a gap between iBook and MacBook Pro, and now they can have that gap. Another possibility is two models; some people want a laptop at the cheapest possible price, and for some the performance is more important. Say $899 and $1099 for basic model with Celeron M and Core Duo. Instead of $1049 for Core Solo.
With these prices, just as an example, I would be very willing to pay $200 extra for Core Duo vs. Celeron M. I would _not_ pay $100 or $150 more for Core Solo.