From MacOS Rumors:
In a near-future version of Classic (most likely introduced with 10.3 or 10.4, well after Apple has moved all new Macs to OS X-only booting), integrated with a corresponding update to the old OS — probably 9.3 — Classic applications will take on an Aqua-ified appearance as well as limited OS X-native features like direct access of some hardware devices through the OS X kernel. OS 9.3 would not be a bootable operating system but would instead be specifically designed to run only under Classic.
Additionally, direct access to Classic’s menubar for use of Control Panels and the like would be eliminated in favor of a new OS X Preferences panel that would integrate most if not all necessary settings functions to replace such Classic-specific controls.