The SID's major difficulties are due to it being an analogue-digitial hybrid. That's why most of the efforts have went down the emulation route, though there's

The SID's major difficulties are due to it being an analogue-digitial hybrid. That's why most of the efforts have went down the emulation route, though there's apparently an FPGA SID replacement in development that's pretty close. The original 6581 is super impractical as each of those is different, but the later 8580 is much more practical to rebuild in FPGA form, even if emulating the analogue side is still awkward.