I think the devs are too busy with fixing up the other tools that depend on API, which usually changes around this time as well
I've poked them in the past, but since as you noted it was missing the last few seasons I've decided to add it to my homepage. I honestly don't know why it's not on every website, on Reddit, on the official Diablo 3 page, and in the launcher. A countdown script takes 2 minutes to create and is so awesome (and necessary, a friend of mine once almost came an hour late to season start).
Maybe they'll add it, I'll poke again, but in the meantime feel free to go to my website ;-) (I do not have any ads or get any revenue or anything for clicks, so I literally couldn't care less, but the more people visit the more inclined I am to keep it up, as I have really limited time these days.)
Awsome! It boosts the hype about a new sesson starting in a simple way. Well you have done alot for this community over the years as it is mate