yeah i seen some people do it with the thermaltake P5, using heavy duty HDTV mounts designed for 80+ inches.
Remember a PC not watercooled can get about 30lbs fully built.
With a custom watercooling solution, it can go even more that. as copper gpu blocks and brass/copper radiators can weigh a lot depending on how large in size you goto.
The key note is how much weight its going to be and planning the proper HDTV mount to use, as the P5 has native mounts on the underside.
My take tho... i would never do it.
Why? simple ... Dust... PC's are in general Dust magnets because they generate EM fields.
So dust bunnies love to collect, not to mention you got fans running all the time on PC, and most of the wall mount cases lack anything close to a filter.
In the end its not worth it.... unless you really have something special to show off with like a holographic Hatsune Miku / Megurine Luka doing there dance inside your PC like this:
The case mod i believe is called snowblind...
However there is a real professional display called the "looking glass display". that ive seen some modders incorporate in some insane projects.
I so want a looking glass display... but they cost 4000 dollars if you can even get one.