This would likely have to be automated with IFTTT at the current time. Flex schedules use the concept of Managed Allowed Depletion, which guestimates the soil moisture based on numerous parameters (Actual/Forecasted Precip, soil type, grade, grass/plant type, sun/shade, sprinkler head precip rate, sprinkler head coverage efficiency, grass/plant root depth, etc).
Incorporating actual soil sensors would be nirvana. Any more info you can share on your product? Do you have an IFTTT channel?
edit: Nevermind, just google Sensoterra. Nice looking product and I'm guessing there is the potential for IFTTT integration with Rachio. However, and this is just my opinion, I think your product (and prices) are more geared towards the professional farm/commercial landscape/golf course and outside the reach of the average Rachio consumer. Curious, what wireless tech do you use for sensor communication?
Maybe a consumer model with zigbee/zwave communication at a lower price point would open you up to the consumer market?