It has always been possible to use an fpga and program it like a cpu and it's software. In other words the chip can be loaded to look like another chip when switching "apps". This post shows a clever use for this. They can load in different old CPUs as needed.

This trick was done in a video processor long ago. An fpga was loaded with a different hardware accelerator for each video transition only when the transition was needed. That was the good-old days when video had crazy wipes and dissolves way too often. Thank goodness those days are gone.