Nest is, in many ways, the most disappointing company. I'm not sure how much of that is just down to them lacking vision or leadership though - they have the skills to do great things.
I had thought maybe they would do a smart lawn watering system next. I know it's a smaller market, but it seemed better aligned with the thermostat as something that could be marketed as a money-saver. The smoke detector doesn't save you any money, it just seems like a solution in search of a problem. The lawn system could basically sell itself: local rebates on the up-front cost, the promise of saving you water/$$, and the name that Nest had already established from their thermostat.
There are some other companies making products like this now, but I don't know if they're good.
The underground sprinkler system my parents installed 30 years ago has a sensor to prevent that, it's certainly not unusual. It would be interesting to see rain sensors for regular sprinters although I'd be shocked if they didn't already exist.