Jumpers are emulated - and available from the 'DIP switches' GUI as W13,W14 and W15. Judging from the ROM code the 3 bits were used to branch into factory test code at boot time (and elsewhere).https://github.com/shattered/retro-bios/...3-022e5-00#L747
As most jumpers drastically alter the code flow i havent found a practical use yet (except for folks able to write custom BOOT ROMs).P.S.: i would not bother too much about the tests at boot time, now the keyboard showstopper is gone (see latest Github entries).
RX50 diagnostic test disk offers more unsettling insights (floppy 'individual test' claims that SEEK_WITH_VERIFY is broken etc.) Possible fixes there could also help TRS-80 users, see WD 1793 problems described by Robbert