I agree. We only have to look 3 years ago to see exactly what happens when those same companies get sideload access. Facebook did something very similar, using their Apple App Store Developer certificate to enroll users as "employees," allowing them to defacto sideload their market research application.
https://news.ycombinator.com/item?id=19033451
I also fully expect the last browser holding against Google's browser monoculture - Safari - to die soon after.
I hate this state of affairs, where Apple's sheer greed is the main force stablizing this fragile environment.