Apple can retain the core design decisions (like the Linux kernel) but the code should be open to pull requests and design improvements. To use Go as an exampl

Apple can retain the core design decisions (like the Linux kernel) but the code should be open to pull requests and design improvements. To use Go as an example, the entire Windows port was done outside of the core team, and is now a supported platform. The same goes for ARM, PPC64 etc. Also, huge performance improvements in core features such as channels were implemented by non Google employees. If Apple open Swift, it can find hold in all sorts of niches they didn't expect it to, and can benefit from an entire community of developers who can fix the language's problems rather than be frustrated by them.