The build scripts (for coreclr, corehost, corefx) are a mess. I worked on getting the build working for Yocto, and there were so many things done differently all over the place. They need a single team to go through their entire build process, top-to-bottom.

Don't get me wrong though, I worked to integrate it into Yocto because I love .NET/C#, but the build system needs a lot of love.