I've seen a few "promising" build toolchains; the sad part is that they need to get significant traction to make real progress. Sincerely, best of luck on build2.

How is build2 as project planning to maintain packages repository for multiple target operation systems? So far all options for Windows I tested looks failed since they didn't get enough traction for 3rd party contributors to maintain packages and library developers have absolutely no interest.

Is using C++ for everything include web interface is sane solution? I could guess reasons for having build bot and web UI in C++, but not sure if it's good way to get more contributors.