There are a lot of wall computers built by people from around the world but it just seems like a complicated thing to do, including all the manual word, woodcutting and so one. It would be awesome if there would be a bracket that you just screw to the wall. This bracket could have spaces for different hardware components which would be attached there by either screwing or locking in with some component cover, or just with dry tape.
There could be a few variants based on what PC components the buyer wants to use, for example one with 2 SSD slots and other with 1 SSD and 2 HDD slots. Hardware that requires special screws to mount, like graphic cards or power can be held on the bracket by using height-adjustable screws. This way there will be more supported hardware components.
The bracket will come with variety of extension cables which would be long enough to connect hardware to motherboard etc. It could be built from metal for extra sturdiness or some sturdy plastic.
This is just an idea, but I think it could be very profitable, because the way computers are built did not change for decades - it's always a brick.