Is this limited to Swift?
Swift Build is a high-level build system based on llbuild with great support for building Swift.
Sounds like this won't help C++ projects?
The requirements of sold developer license, physical mac hardware, and XCode make it hard to be interested or even feel it worthwhile unless you're already a mac user.
Cloud build options only get you so far as well.
I'm very skeptical of sticking to "old and tested" without reasoning.
If you're talking about the implementation, if they're making changes it's no longer "well tested". If it's undocumented, it's not approachable. If you're talking about toolchain, if the old is unapproachable because of inherent toolchain barriers, and custom toolchain dialects, I think it's good to question.
There may also be something to say about them struggling to get new contributors and maintainers (from what I heard/read).