I wonder if the 3rd party issues are intentional or if they are a side effect of the coding.
Some 3rd party issues, like battery compatibility, are intentional.
Others, like the reported ML incompatibility, or lens issues, may not be quite as intentional.
In either event, users purchased the main hardware from Canon.
If Canon is intentionally seeking out ways to create havoc with 3rd party accessories, they must realize that in some instances, it will reduce sales.
I'm sure there are thousands of 7D users that bought the hardware (or, continue to use the hardware) just because it runs Magic Lantern.
Some 3rd party lenses are better than OEM. "Better" can have many meanings. In any event, choice is good. If there are issues with 3rd party lenses with this update, this will make or break promises of service when the stuff doesn't work.
Losing all those battery sales must be a sore point, but maybe there is some validity to saying that the OEM's are priced too high. Someone will always make knockoffs, but maybe if the price was lower for OEM, they would sell more...