The MacBook is a general purpose computing platform. The iPhone and iPad are not. Locking down the Mac will make it unusable for many, many people. It will indeed be the death of the platform, as most devs abandon it entirely.
I personally don't use Homebrew, et al. but, I have a Linux VM which handles that stuff pretty well.
I didn't develop a Mac specific "application" though.
Then again, I only hang around with Mac devs that target iDevices and macOS, using Objective-C, Swift, C++ and Web.
On my Mac circle it is all about store apps and Web apps (Java/.NET Core based).