> The entire point of announcing WebExtensions so early...

Their current schedule only gives a year to build an api, mature the api, get a significant number of popular ported addons, and deprecate their old api. There will either be mature apis and many casualties, or half-conceived apis and lots of addons that will need to be changed with these apis.

With enough time and design, I'm sure this move would result in many positives at the cost of some negatives. But this time frame is just too short for such a huge undertaking.