So physically something small like a lattepanda or raspberry pi would happily fit in there. You could also fit a decent battery inside.
The problems you would need to solve are connecting the touchpad, keyboard and screen to it. Even more fun as that is going to be an old screen.
Depends on how much of the shell you want to keep. Some Bluetooth keyboards would probably fit in the same footprint if you are happy to just cut out the current keyboard and most likely make some kind of border to fit around where the dimensions differ. If you are OK with that then you can probably do similar with the screen.
Although a new screen alone will cost more than this is worth.
