As a PSA to all those who would like this to mean that Gen 2 will get HomeKit turned on at some later date, be warned that this wishful thinking has caused disappointment for other products.
See, for example, some level of outrage when ecobee released a new HomeKit version of their thermostat six months after hinting at possible HomeKit support for the original ecobee3 at CES 2015 (in vague, NDA-inspired-ish language), among other places.
Though I can't blame Rachio for being vague, either (assuming their might be something there), since Chamberlain's MyQ Garage apparently has HomeKit-capable hardware and customers were promised a HomeKit-enabling firmware upgrade over a year ago (again, at CES 2015) which has still not materialized.
Anyway, I'm still hopeful for Rachio HomeKit support in the future, but I've learned that I should be patient and wait for full announcements before I count on it. I realize that Rachio has to keep their proprietery business information to themselves and should not over-promise anything - that just leads to customer frustration and disappointment. And, of course, dealing with Apple means signing non-disclosure agreements and limited information-sharing.
From what I've seen, Rachio is a great, incredibly responsive company and I love their product. Thanks, Franz, for offering as much info as you can!
I'm just putting this out as a warning that a non-promise should be considered a non-promise, nothing more.