I don't think the answer is for Apple to force people into buying custom server hardware any more than it is to force them into making janky rack setups for Mac Minis.
The answer that most people would like to see would be a stripped down, non-GUI macOS that's installable at no cost in virtualization environments, or maybe with some evaluation scheme like Windows Server has, which effectively makes it free for throwaway environments like build agents.
> The answer that most people would like to see would be a stripped down, non-GUI macOS that's installable at no cost in virtualization environments
That's called "Darwin" and it's theoretically open source, but there doesn't seem to be a useful distribution of it. Whether that's due to lack of community interest or lack of Apple support is the question.
A useful distribution (for building anyway) would require all the headers and binaries from macOS, which wouldn’t be distributable, right? So you’d have to have enough of a free system to be able to get to the point where that stuff could be slurped out of a legit macOS installation. Sounds like an interesting challenge.
The answer that most people would like to see would be a stripped down, non-GUI macOS that's installable at no cost in virtualization environments, or maybe with some evaluation scheme like Windows Server has, which effectively makes it free for throwaway environments like build agents.