Making an FPGA-based complete CPU is a mistake even in this day and age as an end-user platform. It's just too easy to pass with emulation. The Amiga chipset is another matter because it works so differently from a modern GPU but a CPU? No chance for a CPU.
Personally, I think an FPGA can supplement an ARM SoC for better chipset emulation by rendering MiniMig graphics to a texture map so the RTG core can put it in a window.
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