Light but stiff internal subframe which can rigidly hold the motherboard (in my case an upgraded SKR 1.4 Turbo but has same hole spacing as original board) and a raspberry pi for running Octo Print all neatly inside the original housing.
Frame is designed such that the fan is below the RPi USB ports and away from the GPIO pins such that it doesn't collide with anything. For wifi I use an external antenna which is placed in the original USB slot (I desoldered the original USB port as mine was already broken anyway due to the bad quality plastic).
If you want to power the raspberry pi from the motherboard, an additional DCDC converter is required due to the current demand of the Pi. I power the Pi from the neopixel LED interface. If you want to use the original motherboard I think you will have to use a dedicated power supply for the Pi.
I used a PCB standoff in the upper left corner of the pi to prevent it from sagging, but this is optional as the frame is stiff enough to hold the pi without sag. The USB type B slot can be used to elegantly route a camera/webcam to the pi.