Please enumerate considered alternatives in Explainers

[slightlyoff]

The Plane Detection API explainer currently lacks a section on considered alternatives. Knowing the depth of the design thinking helps give everyone (including Blink API OWNERS) confidence in designs.

[cabanier]

@bialpio wrote an explainer on various approaches to deliver the plane information.
I'm slightly in favor of difference lists but he told me that it can be emulated with his proposal.