Aesthetically I like the current design, even the trackpad really is big enough. The keyboard is fine, designwise and responsively. Round slightly the top edge where the palmrest and palms/wrists come in contact - the sharpish edge has bugged me slightly. It would be nice if the user surfaces (keyboard/palmrest, etc. were actually metal and not colored plastic. The textured paint on the keys, especially the spacebar seems to wear faster than I'd like, but I am a prolific typist so maybe that's asking a bit much.
It's a pro model - so make the hard drive user accessible for upgrades, like the A series IBM Thinkpads. One screw, pull the side latch and out she comes, remove hd from carrier (four screws,) replace w/ new drive, insert into laptop, one screw (can use a coin) and you're done. Also, some design that would allow the optical drive bay to be upgraded with newer drives, like blueray or faster drives in the future. IBM had this feature on their pro-laptops for years called the ultrabay 2000, and tons of peripherals could be swapped out there, including extra battery. Since it's a "pro" machine, and Apple is looking at penetrating the enterprise market, don't worry about making it thinner, just make it more durable, and easily serviced by IT departments with quick-replace parts (more modular.)
Also, a HD variant on the 15.4" model.
Finally, perhaps a redesign on the hinge mechanism to allow the screen to be tilted back at a more radical angle.
So, to summarize.... make it tougher, more modular for user/IT upgrades, HD and better hinge angles. No chicklet keyboards, default model remains matte display, slightly softened edges, maintain minimalist design.