JDW, I brought this up here before.
My understanding is that it specifically addresses a revised stepper motor in the Sony 400K drives. There were two basic types of disk drives: Early Sony model OA-D34V (shipped with ROM version 342-0220/0221-A).
Later Sony models OA-D34V-02 or OA-D34V-22. These models had a new insert/eject mechanism (shipped with ROM version 342-0220/0221-B, these drives were incompatible with ROM version A).
There may have been some other minor changes, but this seems to be the primary motivation for it.
Henry do you mean the ROM interaction with Macsbug? As the 64K ROM did not have a debugger built-in like the 128K ROM.
Of course Jobs was still firmly driving the boat at that time, so there would have been no chance for a >512K RAM fix. I'm sure Jobs even fought the stepper motor fix, since it only proved him wrong.