Presumably Apple is dropping x86-32 because they don't want to spend resources maintaining 32-bit support libraries, doubling their testing matrix etc. And now you want them to add a third ABI?
(Even in the Linux world, which prides itself in supporting crap used by a handful of people globally, X32 is dead, to the extent it was ever alive.)
X32 is dead exactly because, where 64bit is not needed, x86-32 is perfectly fine. I.e. the only practical reason not to go 64 is backward compatibility.
- Never needs more than 4 GB RAM (because it's not worth the usability downsides from having two binaries and letting the user choose which to use, just for a small performance boost)
- Is performance critical
- Performance is bound by memory and/or cache bandwidth
- A large share of the program memory usage is due to pointers
The intersection of all the above is just vanishingly small in reality. X32 was never more than a gimmick to score a few extra points in SPECcpu. And thus people rightfully ignored it.
(Even in the Linux world, which prides itself in supporting crap used by a handful of people globally, X32 is dead, to the extent it was ever alive.)