It’s worth mentioning how simple the computer is. While the Gigatron is an 8-bit computer running at ~8 MHz (and probably more powerful than an 8086), it only has... seventeen instructions (with a few encodings for different operands). The instruction set is so limited, they created Gigatron Control Language (GCL) to allow you to write in a slightly higher level assembly.

So getting an emulator running is quite an achievement.

Getting an 6502 emulator up and running is not too difficult and you saw how the author did it "quickly" which I took to mean in a couple of days / a week.

I don't really see this as similar to the way many of FPGA applications are done these days. The approach in FPGA is more along the lines of implementing the same logic as the original CPU as opposed to microcoding / emulation.

I guess I could be more clear. In industrial FPGA applications the goal usually isn't the CPU, the goal is to implement the required logic while keeping the number the gates needed for this to a minimum, and implementing a simple CPU (a.k.a. PSM) is what makes it possible. Same here: the CPU only serves as the economical way to implement something else (another CPU, in this case).