smf is correct: by definition, if floppy operation on the hardware is correct and doesn't randomly fail all the time, then obviously the operating systems do not cause trouble with the arbitration. And therefore there is no need to emulate it in order to get them to boot and run.
ETA: There is one wrinkle, though.
WAIT is also used When the RX50 board decides it needs additional time.
Some systems in MESS cannot currently be emulated because they wire the WDx7xx so that it halts the CPU when its busy, and then the firmware/software doesn't need to ever busy-wait for the controller. If the RX50 is actually wired that way, you might be in trouble, but the fact that multiple OSes do boot already suggests that that isn't the case. It would be useful to trace on the schematics exactly what causes the RX50 to assert WAIT though.
Last edited by R. Belmont; 05/20/14 12:15 PM.