This build demonstrate what’s actually interesting about FPGA to me. A pure implementation might as well be a software emulator. Being able to interface real chips makes this really neat.

The author used the lattice fpga for exactly what it was designed for: glue logic. This fpga type isn't what you'd throw a couple of cpu cores on, it's more along the lines of replacing a few dozen 74xx series logic chips. I personally enjoyed the author using modern day chip equivalents instead of soft cores on an fpga. I find the latter to be much less interesting.

Good point. I was thinking why he didn't just do the V20 etc. on the FPGA, but then a software emulator would be more flexible. Having a real hardware interface that has the right timing is something software would have to work very hard to do. Using an FPGA also forces the designer to more or less really understand the original hardware design, not just the software-visible effects as an emulator author can get away with.