@Riley_S Ok, thanks for the info. Looks like I'm going to be going with Leviton's solution. They do motion 3-way (and 4-way). All wifi, looks like a nice, complete solution.

@Riley_S Wait, the motion sensors aren't ultrasonic? They respond to light changes???

I see 3-way smart switches. Which are awesome. Why no 3-way motion switches? I can take two 3-way switches and convert one of them to a single-pole motion detector, but I'd like to have TWO 3-way...