Can you point to specific issues with the current build system?

It seems to me that for 1. it will only make it easier for projects that use CMake, 2. the build system is not the only part needed to support a new OS and for 3. I've not found Python to be particularly slow to build for such a large program. You may want to look at ccache if you want to speed you build process (I'm not using it on this computer and it's still quite fast, Make will only rebuild the appropriate object files already unless you explicitly clean them).

Before making large changes to the build system, you should open a thread on the python-ideas mailing list, there was some discussion about this a few years back but maybe now that Python2 is gone it would be easier to make this change?