Isn't the 486 ISA (and whole surrounding architecture really) royalty free by now? I wish we'd get cheap chinese 486 clones like the knock-off Arduinos.
Imagine paying < $10 for a 486-compatible SBC for all your retro nerd needs. Yes, I know you can emulate it on a $25 Raspberry Pi, but it's not the same.
There's a 486 open core under a BSD-ish license: https://github.com/alfikpl/ao486 I have this on an FPGA and it can run DOOM albeit a bit slowly.