Overall I think this is pretty solid. Blizzard might even already have some type of internal document with info/drop rates for new events already, but I think it’s good to put this out there regardless.
I’m definitely in favor of having most items obtainable if someone puts in the time and effort to do the holiday/event dailies. There can be an item or two that aren’t guaranteed but have an increased chance on the first event encounter of the day for the account so that people don’t feel like they have to grind it on 30+ characters a day. The drop rate could be increased slightly if the event is annual, so if it had a 1% drop in year 1, it could have a 2% in year 2, 3% in year 3, etc, to make it a bit more likely to drop but by no means guaranteed.
Of course, the Trading Post now gives a great outlet for certain items if people missed them during the holiday or anniversary event. There’s a lot that they can do with this and hopefully they take advantage of it.