Which airline wants to be the first to test the revised system?
I'm going to be brutally honest: Every operator will need to have this software installed.
Airplanes make money when they are flying (and not flying INTO).
The good news to this is every MAX pilot will now be armed with knowledge and skill to disable MCAS. Who knows, maybe pilots who didn't get simulator time (for the new "revised" syllabus with MCAS included) will/might just disable MCAS during (or immediately after) take-off.