Guess I'll come in with my two cents.
For the short term:
Removable ODD as a Built-to-order. Instead of listening to the dead man (as much as he was respected, he isn't here any longer to predict trends of the future..) and this will allow buyers to configure DVD or BD drives, select from a conventional spinning drive / SSD, or perhaps a larger battery. Heck, Apple might as well buy out MCTech and internalize and apple-ise the optibay.
Things I'd be keen for, but would probably involve structural / chassis change...
- 4 RAM slots. Dell and HP both offer that, and for those of us who require the Pro for intensive applications (unlike those wanting to flatten it into an air

), the affordability and ease of accessing 16GB of RAM, which really isn't hard to burn with a small number of demanding apps is great. 32GB opens future-proof possibilities and anyone like me who doesn't upgrade every minor refresh (or four) will appreciate.
- Removing the clock, etc off the 'main screen' and positioning it near the keyboard. This would definitely involve a lot more change. Likewise, having a litttle screen much like the top screen of SLR cameras, giving quick access to information from the time, CPU usage, fan controllers and the current user account would free up space for more menus, a whole new UI, or allow easy access when using Lion's new full-screen mode. (I've had this idea for quite a while now and Lion's full-screen just gave more reason to implement it!)
- Rear-mounted camera. All of us who carry our laptops with us on the move, trying to capture the moments on the go. This makes sense doesn't it?
- Addition of a CF card slot (Maybe a customisable input slot, much like a built-in card reader. If it can be replaced, it could open possibilities to anything from additional USB ports, another SD slot, CF, P2, and who knows...)
- A docking station. This one's definitely been said before, but being able to come home and hook my laptop up to desktop-standard performance and a good chunk of storage is definitely a must! (Bigger monitor a bonus)
- GPS antenna perhaps?
- More appropriate as a BTO order... replacing the keyboard with what Acer's done - an identical-sized touchscreen in place of the keyboard.
Many more ideas, but I'm sure Tim Cook needs a bit of time to get his bum marks ingrained on the mighty Apple iThrone...