I'm not sure. I think there continue to be reasonable uses of the three-flag state system, even if we're not currently using it in MediaWiki.

The visual distinction of constructive/progressive hasn't shown to provide users advantage in it's original, theoretical concept and following confusing implementation: T110555.
Although the idea of another flag is technically powerful. it's currently neither useful nor needed.
When activating MonoBook and going trough Visual Editor's Apex user interface, the remaining, slightly prominent instance I came across, where the constructive flag is used is the “Insert“ button of dialogs like “Hieroglyphs” or “Gallery”.

From all what's left, we should not hesitate to switch them over and get rid of the “constructive“ flag in the library and probably consider to re-invent it when coming up with a different use case/facing a clearer user experience need.

Another point, not to be left out, is, we're imposing a decision on developers that has no functional and apart from Apex, no visual implications any more.
One of the examples for it being confusing is T163623.

Change 355898 had a related patch set uploaded (by VolkerE; owner: VolkerE):
[oojs/ui@master] [DEPRECATING CHANGE]: Deprecate constructive flag

https://gerrit.wikimedia.org/r/355898

Next confusion: https://gerrit.wikimedia.org/r/#/c/354744/1/

Change 380795 had a related patch set uploaded (by Jforrester; owner: Jforrester):
[oojs/ui@master] [BREAKING CHANGE] Drop the constructive flag entirely

https://gerrit.wikimedia.org/r/380795

Change 355898 merged by jenkins-bot:
[oojs/ui@master] [DEPRECATING CHANGE]: Apex theme: Begin killing constructive flag

https://gerrit.wikimedia.org/r/355898

Change 380795 merged by jenkins-bot:
[oojs/ui@master] [BREAKING CHANGE] Drop the constructive flag entirely

https://gerrit.wikimedia.org/r/380795