Alternative Super I/O Controller
If one wanted to create a new kernel debugger board, the Microchip LPC47N217 Super I/O Controller is still in production and has a configuration interface compatible with the SMSC LPC47M157. It has fewer pins, thanks to a reduced number of logical devices, so should be easier to solder. Turns out the LPC47N217's configuration registers are not compatible, after all. Its register I/O sequence is also slightly different, so the kernel would have to be patched.