Two points: - Presumably there's a preference to be pessimistic on schedules so they don't have to go through the process of being re-chartered if things drag

Two points: - Presumably there's a preference to be pessimistic on schedules so they don't have to go through the process of being re-chartered if things drag on unexpectedly. - By the time the standard is wrapped up, you'd expect the major browser vendors to have had fully production-ready implementations for a while, just waiting on any final tweaks. (Also, v1 is supposed to have achieved recommendation status by Q2 2018.)