I'm a bit unclear what you seem to think is lost under these circumstances versus copylefted software. Let's say Apple released Swift under the GPL. They would still be free to do all of the things you describe.
So as a developer right now, given that you have a plethora of open tools and an open ecosystem, why would you choose to use a language where a company has the opportunity to manipulate you in the future?
This is, as above, no different from the copyleft case.
So as a developer right now, given that you have a plethora of open tools and an open ecosystem, why would you choose to use a language where a company has the opportunity to manipulate you in the future?
It's extraordinary difficult to argue that Apple would be in a position to manipulate me as a developer if I started using Swift. For one thing, once the code is open-source – that's it. I can continue developing software using that language. If Apple decide not to release new features, and instead keep them proprietary, then the community is free to fork development.
More importantly, if it's important to members of the free software community, they are entirely able to develop capital-F-free software on top of Apple's release!
I'm really thankful for copyleft licensing and the amazing tools it's given us. But it's a vary complex issue, and I just don't agree that release under a license with fewer restrictions is necessarily a bad thing!