I prefer Rust to Swift personally - the language is simply better.
As for Vulkan, Apple and MS didn't just wake up suddenly to make Metal and DX12. For years they didn't care and now suddenly both decided to wake up? No, it started with AMD saying that they want to open up Mantle. That's when Apple rushed to make Metal, and MS rushed to make DX12. They both borrowed a lot from Mantle for the reference. So no, it's Apple's fault that they decided not to go along with everyone, and push their own lock-in. It's not surprising though. Lock-in mentality is common for them.
I prefer Java and C#... but Swift open source is still a good thing and a good contribution to open source.
Metal is an API created for iOS, it was ported for OS X to create an environment, I still think is logic to believe that Apple made a logic choice, this was a choice made for Apple developer to make it easy to port iOS games to OSX. Also there is still a supported OpenGL version and I still think it will get an update, so I don't think they made a lock-in at all.
As usual, the open source fans have just a lot of prejudice against apple (but only few prejudice against microsoft).
I use a lots of open source applications on my macbook right now (Blender, Firefox, libre office, VLC etc...)... And I'm sure most videogames are closed source even on Linux.
OSX for sure have a lock-in (you can only install osx and get official support on a mac), but there is no real lock-in difference from windows when you look at the software.
When you look at mobile, there is no real open source even on Android. Applications are tied all to official stores.
I repeat, I will not defend apple at all costs, there are a lot of things that are wrong in their choices. SIP is one of them, create a security system that can be only be deactivated without the possibility to create a whitelist is not a good way of create a security system. the fact that an application can go offline even from your purchase and you need to make a backup or you can lose it forever is not a good at all.
Also I prefer a NVidia graphic card, I don't want to buy a new mac if they use an AMD.
there are many things that I don't like about apple and osx, but Metal is not one of them.
Anyway, the point is: I'm sure they can port the witcher 3 for linux AND mac if they want, eON or Feral or native port or something else... they can do that right now.
Also I'm sure they want to make a mac port before or with a linux port... I'm sure there will be no linux before mac (almost sure).
Finally there is no point in ask for a linux version alone. I understand you hate apple because "open source fan need to hate apple" (an open source fan that want to play the witcher 3 that even on linux will be close source)... but still there is no point in ask just a linux version, it will will never happen.
That's why in this topic I ask for a Mac and Linux version, I would like to buy the witcher 3 and play it wherever I want...if it was possible even on ios AND Android.
If this is not possible I will wait until wine dx 11 or a really late eON port, but I will pay something like 2€ (like I paid the witcher 1 and the witcher 2).
I don't think Apple is "evil"... I don't think Microsoft is "evil"... And I will always use windows, osx and ubuntu (ubuntu because arch linux is really a nerd thing with no real use) if possible (for sure with no mac I will not use osx much).
I use linux because I like it, not because osx and windows are bad and evil.
Finally have you ever heard of a developer that choice something like Rush or Moltengl? Rush and Moltengl are experiment... not something you can use in real life (experiments that you need to pay).