I looked closely at FPGAs and they have their pros, but they add a lot of complexity as well. Keep in mind that the original idea with this was to be able to load the entire system onto a cheap board and be able to test it on the bench without any extra hardware (Obviously not on an engine).
The other major reason not to use one is simply because these days I'm not sure they're really needed. The 'high speed' inputs to an ECU really aren't that fast, even at the highest end you're only looking at somewhere around 16Khz. With high speed MCUs (70+Mhz) available for a couple of dollars, the value in the FPGA is somewhat limited given the complexity of adding them.
Comments
I looked closely at FPGAs and they have their pros, but they add a lot of complexity as well. Keep in mind that the original idea with this was to be able to load the entire system onto a cheap board and be able to test it on the bench without any extra hardware (Obviously not on an engine).
The other major reason not to use one is simply because these days I'm not sure they're really needed. The 'high speed' inputs to an ECU really aren't that fast, even at the highest end you're only looking at somewhere around 16Khz. With high speed MCUs (70+Mhz) available for a couple of dollars, the value in the FPGA is somewhat limited given the complexity of adding them.