[Timwi]

As someone who doesn't follow the standardization process, I would love an explanation how proposals like this fail even when they have widespread support and no downsides. Is there an easy answer to this or is it different from case to case?

[lyptt]

From what I've seen, standards need to be picked up by browser vendors for them to become established.

Usually one vendor will implement it behind a flag, and if it gains traction then other vendors will follow suit before it becomes a generally available feature.