Overconstrained

I have made this case before, but I believe that it is worth repeating.

Constraints present a very complicated API.  I do not believe that
there are real use cases that cannot be supported with mandatory
constraints and a number of attempts to change those mandatory
constraints.

I would like to propose that we remove optional constraints.

Sure, it's relatively easy to contrive examples, but I don't believe
that there is anything that a real-world application would unable to
do using a mandatory-only constraints API.

To add to this, a lot of the new features we are dicussing
(capabilities, better device information) only makes optional
constraints less relevant.

If we retain these, I'd like to see better justification for their existence.

--Martin