Of course they tested Doom :-D

They might also run Linux kernel 3.7, that supported i386. Gray386linux is still maintained, and runs a patched 3.7 kernel.

https://github.com/marmolak/gray386linux

Question: Are there today any 386 instances running somewhere in the basement to do some productive stuff, maybe processing only some controller data once a day?

I remember the link some month ago where that one small shop ran completely on an old Amiga (?IIRC, not sure, was linked here)

Around 98/99 I was involved in a small IT-management company serving SME around the region, we had a client producing distinct metal objects with a big press; this got feeded once a day with a 5.25 floppy from another machine with production data - and it was still in use while we had already ethernet/USB/3.5 floppies etc. :-D

Kind of surprised this only takes 18K LUTs. That's a fairly small FPGA these days.

Did the microcode disassembly find any useful backdoors to read microcode without decapping?