Zwift bundled workouts are not text based but in one a binary file. You can extract them to an XML manually via user interface and then modify. If you know a way to extract them programmatically or in some other way from the .wad file, please let me know.
About the change request. Zwift would only need to do 2 things:
- change the default (implicit) value of this flag from false to true in code. That’s one/few characters in one file. If their code is somewhat reasonable.
- reposition the display of average because it currently overlaps with “increase/decrease speed/cadence” message.
Anyway, never mind, I realized I’m not going to see an improvement by Zwift based on what I’ve seen so far, so I spent half an hour to create a script for myself that adds explicit attribute to every step of every .zwo file. Still have to manually extract each workout as I didn’t see a quick way to extract them from the workouts.wad binary file. Again, if anyone knows how, please let me know. And still, I cannot move the location of the average display 
And the 1% user base isn’t really a factor, here’s an example of feature that 99% of the user base has wanted since the beginning and it still hasn’t been done :D: Allow Saves Without Exit