I dunno. Each of these physical processors have 8 kilobytes SRAM and 62 kilobytes of some kind of flash or something. Multiply by 4096, wouldn't that be one hell of an FPGA?
You can buy Xilinx FPGAs on PCIe cards that could easily handle THOUSANDS of RISC-V cores.
Almost all FPGA dev boards include DDR memory so you could also put code there if you needed to.