Yeah, I think random-instruction-sequence testing is a pretty good approach to try to find the problems you didn't think of up front. I wrote a very simple tool for this years ago to help flush out bugs in QEMU: https://gitlab.com/pm215/risu

Though the bugs we were looking to catch there were definitely not the multiple-interacting-subsystems type, and more just the "corner cases in input data values in floating point instructions" variety.