The PowerMac revisions must come before the iMacs are upgraded. Since I haven't heard much talk of new processors from IBM, I can't say for sure when this would be. The iMac's only been four months since its release so I wouldn't count on one soon, at least not within the next few months. And even if there is a revision, I wouldn't count on much of a GPU upgrade. It is a consumer computer, and Apple seems intent (at least based on its history) to keep it that way with a lower-level graphics card.