The opposite of turning an Ikea coffee table into a server rack has to be turning an Apple Xserve into a coffee table:
https://www.reddit.com/r/homelab/comments/kig3gw/do_coffee_t...
https://www.reddit.com/r/homelab/comments/kig3gw/do_coffee_t...
On the other hand, there are computers with a form factor that allows direct reuse as a table or sideboard, like the Connection Machine CM2 (smaller than it looks in most photographs) or the less curvy SGI Onyx and Onyx2 models (the perfect size for bedside use).