Would be cool if they did, but they've just upgraded PB's to 128MB (which is optional, standard is still 64MB). So I would highly doubt they would upgrade in the near future.
Man, I really wish that they would though... I mean, the chips are out there, and the PBs could really be taken more seriously as desktop replacements with this step up. Seems like it'd be an easy upgrade to me (keeping in mind I'm very naive when it comes to the complexities of Apple hardware/software
). The upgrade from the 64MB to the 128MB card is only $50 on Apple's site. For that price, even if I wasn't big on graphics performance, I mean, it's only 50 bucks! Why wouldn't anybody upgrade even just to simply extend the life of their PB? The Aqua GUI depends upon your video card for its elegant look, so future OS upgrades will probably require even more graphics capabilities, such as a step towards SUN Microsystems' "Looking Glass" GUI.
As for the jump to 256MB, even if it cost $100+ on top of the 128...it's twice the memory! Over all, it'd be a drop in the bucket for the price of a PB, but plenty would opt for it. As a mobile chip, the 256 actually only has the processing power of (roughly) their 128MB desktop graphics cards. If we can't expect to see a G5 in a laptop anytime soon, then I think the next revision should include this option... if not sooner