I really like the addition of the web camera - it's a nice bonus on top of the more traditional temperature/humidity/light/moisture readings that most people incorporate into these DIY systems. Much better than what I made the first time I built one of these things.[0]

The one thing that made my scratch my head was your approach to measuring moisture. There are several very reliable methods for measuring soil moisture directly (changes in resistance, capacitance, time domain reflectometry, etc) that will give you exactly what you are looking for here.

"Therefore, we felt it was fair to assume that watering based on moisture level is impossible and that GreenPiThumb is doing the best it possibly can, given certain inexorable limits of the physical world."

This just isn't true. The sensor you picked up from Sparkfun should give you decent measurements for a while before degrading gradually depending on your soil chemistry.

[0] I ran a consumer soil moisture IOT company for a few years that was sold to Scotts Miracle Gro in 2016.