Why this half backed open SoC? The CPU has an open source instruction set while the FPGA is complete proprietary garbage.
All FPGAs are "proprietary garbage". Some have been reverse-engineered (like the Lattice) with great effort, but that's the only difference.
Well by that strict definition all of them are indeed proprietary. But in effect some Lattice and Xilinx FPGAs are usable as if they were not proprietary.