The changes were announced ahead of time, but within the discussion there hasn't really been actual consideration around not switching back to MSBuild. They've been pretty set on the it within the Github issues (#1433) and haven't provided too much reasoning for it outside of tooling. Of course it's not that alone either there is just a bunch of confusion around it right now on the direction of .NET Core.
From one of the end comments:
> If you want to work out how it should be made and be in the design team that talks about it... please do. [Link to MS Career Page]