I think my final solution to using prebuilt libs on Android is going to look like this:
After a new release of cocos, I do a full build once of one of my games.
The .a cocos libs build during this, I'll move to a "higher" folder, so they can be accessed by all games.
I''ll write my own .mk file that I will call to import those libs (only has to be done once, ever).
This should result in the exact same .so result.
It will be much faster, because I don't need to prebuilt all libs (since there are a ton I don't need/use).
It will be catered for my exact specific wishes/requirements.
The only downside is, that it's only 100% save to do, for all games that use the same APP_CPPFLAGS. But that's the case for me, so no worries