At least as this is software for developers, I reckon most won't mind buying it outside the appstore, it sounds really useful.
I like to think this is a foulup and will be fixed soon. However, XCode 8's help system is massively improved and this might be a case of Apple trying to force developers down that route. Which is a bloody shame. I really hope this is just some screwup :(
It works quite well for me.
Like code signing. Or the encrypt-then-compress DRM adding many MB to binary sizes. Or code signing causing pre-main startup times to bloat. Etc, etc.
Developers will continue using and supporting Apple products regardless. We hear a story like this at least three or four times a year.
Geeks love their Apple products far too much to ever walk away no matter what Apple does.