There's a min/max line on the unit, but it probably can go 8-9" into the liquid. I don't actually use it directly in the mash. I recirculate through a 10-gallon cooler with a pump, into a coil in the kettle, and the Anova heats the water in the kettle to the target temperature. And since I have a kettle full of hot water at that point, I just use that for sparging. If I'm just heating strike or sparge water without the HERMS set-up, I try to keep the water to less than 5 gallons each and heat it in a 5-gallon kettle, which fits it just fine.
I'd think that you could come up with a simple bracket that would drop the unit far enough into the kettle to keep the liquid level appropriate. Especially with the wifi unit, you could set the unit to start early in the morning so that you wake up to heated strike water. Makes the brew day start that much better to wake up to hot strike water!