not counting /sys/src/9/pc/*.root.s, the assembly code in the system including libraries is perhaps
1500 to 2000 lines (mostly little hand-optimised functions in the libraries, and chunks of code
for the machine-level support for bootstrap and kernel).  so that seems a waste of time to change.
a real-mode assembler would indeed be easier than the #defines for the few dozen lines of
code that needs them but otherwise, not.  and if, as i understand it, the assembler is itself
written in assembler, that seems rather unattractive here.

just my own feelings about it.