Nostalgia Nerd's video about beige cases got the lion kingdom pondering stuffing a modern computer inside a 1990's UNIX workstation case.  It wouldn't be a single board or budget item, but something equivalent to its peers that a 1990's UNIX box was to its peers.  The HP 9000 & Sparcstation cases exuded raw, uncontaminated computing power that consumer products either didn't have or  lost to crippled operating systems.  

Fitting a modern heat sink & graphics card in would be hard.  The Sparcstation case would definitely be too small.  The HP 9000 C360 had the largest case & it would still be hard to fit into.  The C360 looked a bit too much like a consumer product.  The venerable 715/100 was what the lion kingdom's generation started their power user experience on & had a taller case than most 1990's workstations.  There are still PCIE angle cards.  Water cooling might reduce the space.  The power supply would have to be a flat server size.

Then of course, there are now multiple hard drives where those old boxes only had 1.

The mane problem is all the classic UNIX boxes went under the monitor.  They used a lot of desk room & couldn't be moved around as lions now do with their monitors.  Lions didn't eat at their desks, in the old days, so they didn't have to move anything around.

The only way it could become practical is if the lion kingdom replicated the case, since actual HP 9000 boxes from 30 years ago are crazy expensive.  The space limitation would limit it to a downgraded single board computer, not for regular use.  It would be limited to some kind of appliance.  Today's single board computers are still way beyond the original HP 9000.