One of the important parts in the post seems to be that it is not just a C++ build system, there are many other tasks executed through the build system. In that sense, it seems like build2 isn't a great fit.
[1] https://build2.org/build2/doc/build2-build-system-manual.xht...
My impression about the modules you linked to: A secondary feature because many C/C++ project need some additional scripting.