Very good thinking on the coverage map! That's certainly a much simpler solution than I envisioned. And for this purpose it's an elegant solution.
I'm not sure how the big companies do coverage maps. I suspect they are storing periodic point data rather than coverage pixels because I can forget to turn off recording on my tractor and record paths all over my farm without consume a lot of space.
What are you currently using to interface with the implements sectional controls? Are you using an Arduino in the loop somewhere?