No one knows. However the roadmap for the mobility 6k series looks promising-- it even shows blackcomb as having 256bit bus+ gddr5 ram. That would be a real good option for iMac, effectively doubling memory bandwidth from 64gb/s to 120+, providing a huge increase in performance. It all depends if apple's gonna spring for that tho.
Mobility 5k series was shafted, because AMD never based the high end mobility 5k series on their cypress chip-- only juniper.