Yes, it's hilarious how many people took the trouble to explain how they really wanted to buy a Rachio system but did not when they realized it did not support HomeKit... why would they post again anyway, until units came out that supported HomeKit? Many of them might return, and start posting, when Rachio supports HomeKit - in fact I would hope the company would email each of those accounts (including mine) if they ever do announce support.
I really like how Rachio works, I have a friend who has the system and really likes it. But at this point I'm not buying new smart systems from the home unless they support HomeKit, and I thought it was important to let the company know another person is not going to buy a unit until they know it will be supported (even if the hardware shipped earlier without support initially but it could be added later via update, I'd be in).
I didn't see a lot of people respond much to why they wanted HomeKit integration, so I thought I'd expand on my reasons - basically what I want out of the system is the possibility of control and examination of data from other apps. Like what if I wanted to wire in moisture sensors to some parts of the lawn and trigger extra watering if they didn't get enough from the normal watering stations? Or I might have a console alerting me to any problems across the whole house, in which a Rachio alarm might be one of many items...
The Rachio app is really nice, and I'm sure I'd use it. But like I said I want the possibility to use that data across other apps as well, or to be able to control the system in other ways or for other reasons.
Also as someone else noted, smart device security is growing more and more important and while it may seem strange to think about security from something like a sprinkler system, if an attacker got in they could potentially use the sprinkler controller as a bridge to break into other computers in the house, or also launch DOS attacks on websites from as part of a botnet (as they have done with many, many internet connected webcams). Being part of HomeKit means more than just the "Apple Logo" which was referred to at some point, it means a certification of a certain level of security.