Re: NBSP supposed to stretch, right?

So it follows that any justification operation should treat NO-BREAK SPACE and SPACE identically.

And any recommendation that is not compatible with what the overwhelming majority of software has been doing should be ignored (or only enabled on explicit user input).

Otherwise, you'll just advocating for a massively breaking change.

NBSP has been supported since way before Unicode. It's way past the point where we can legislate behavior other than the de-facto consensus among implementations.

Now, if someone can show us that there are widespread implementations that follow the above recommendation and have no interoperability issues with HTML then I may change my tune.

A./