i will try to keep my points divided, as i tend to ramble..
1. motorized screens are very typically unreliable. to date, all of the single din motorized screens that take a vga input(short of the revo-sys unit because no-one has posted a test of it) have, or used to have serious problems operating reliably. the lilliputs are known for stripping the plastic gears that lift the screen and the zenarcs are known for the control cable going between the screen and the control board to break from screen movement.
i realize it is not your intention to copy, or use either of these designs, this is a warning that many motorized screens do not work as intended..
2. in following with point #1, most 7" vga screens are over 0.5" deep. and because the electronics in them were never meant deal with motion, i fear that if you separate the main-board from the screen--to get screen as slim as possible to fit everything in a motorized chassis, you would end up having a similar issue as the problem with the zenarcs-- creating a service nightmare for yourself..
3. i have never seen any company offering a motorized chassis only for a single din screens.. though i imagine that you would need to pay attention to the weight tolerances of the design, otherwise, you would have the same problem as the lilliputs have-- stripping gears..
i do remember one member modified a used motorized screen chassis to hold a vga screen, but don't remember the forum name.. but you already said a option like this is out of the question..