This is a great proposal. Thanks for sharing!
I know Wyze plans to dedicate this year mostly toward cameras and app updates, etc, but I hope that next year they will seriously consider trying to update the sprinkler controller in the way you suggest here which would allow them to do it with just the same hardware they already have. That would be really cool! If I ever consider adding sprinklers to my backyard I would totally love to have it set up as you describe with a secondary controller and the AI being able to use both as if they were one.