I am going to defer this past 7.3.0, since it didn't build, and I want to see how it affects builds on Windows, which some people do.

Yup, it's waiting on the CPX PR, which needs a merge and release.
adafruit/Adafruit_CircuitPython_CircuitPlayground#117

I tested this successfully with a custom build using the branch from adafruit/Adafruit_CircuitPython_CircuitPlayground#117 on a CPX. I ran many of the examples from this guide: https://learn.adafruit.com/circuitpython-made-easy-on-circuit-playground-express/circuit-playground-express-library and found them working as expected.

On the CPX builds using current repo the remaining free space for an English language build was:

251864 bytes used, 1576 bytes free in flash firmware space out of 253440 bytes (247.5kB).
11856 bytes used, 20912 bytes free in ram for stack and heap out of 32768 bytes (32.0kB).

With the modification to use the branch from this PR the space is:

247448 bytes used, 5992 bytes free in flash firmware space out of 253440 bytes (247.5kB).
11856 bytes used, 20912 bytes free in ram for stack and heap out of 32768 bytes (32.0kB).

So this does seem like a decent chunk of space savings.

Thanks for figuring this out @Neradoc! this will allow more helpful features to fit in these builds.

I believe the difference in space that you find might be in part due to the fact that the Circuitpython PR has not been rebased on latest. And neither has the library PR. Here is what I get when I make sure to pick the right ones:

247828 bytes used, 5612 bytes free in flash firmware space out of 253440 bytes (247.5kB).
246772 bytes used, 6668 bytes free in flash firmware space out of 253440 bytes (247.5kB).

That's 1056 bytes saved. The latest bundle's bluefruit.mpy is 1222 bytes, so that's in the ballpark of my expectations.