You've probably seen this already, but just in case... You might be interested in Bunny Huang's work on Betrusted and Precursor. He's building a soft-core FPGA

You've probably seen this already, but just in case... You might be interested in Bunny Huang's work on Betrusted and Precursor. He's building a soft-core FPGA based on RiscV instead of i486, but it's a fascinating project: https://betrusted.io/ https://betrusted.io/ - which includes an open source RiscV design that runs on an fpga https://www.crowdsupply.com/sutajio-kosagi/precursor https://www.crowdsupply.com/sutajio-kosagi/precursor - an FPGA-based open hardware implementation you can buy and experiment with