I don’t think that the FPGA based emulation will be “correct essentially for free”. The FPGA emulation itself is a lot more labor-intensive to create in the fir

I don’t think that the FPGA based emulation will be “correct essentially for free”. The FPGA emulation itself is a lot more labor-intensive to create in the first place. In order to make it work equivalently to original hardware, you will need to accurately understand how the original hardware works, which is something you would need for software implementations too. In general, software has a much lower cost of development than the cost of developing something for FPGA, and if you had something like a Verilog implementation of your emulator, it is not necessarily true that you need to run it on an FPGA—you can run it in software, or use it to verify a software implementation. I think the real argument here for FPGAs is that some things are tricky to emulate with reasonable speed and accuracy in software. I don’t think the other arguments hold up—for example, arguments about latency—since the time scales involved are fairly generous (16ms to generate a frame of video).