Say what you want about their Windows and Office divisions, they put a lot of effort and resources into their development tool side. Being able to direct the development Electron, the way a lot of desktop applications are being written in 201X, is a clear advantage to them commercially. They also have the ability and resources to solve some of the problems that have plagued Electron/NW like resource use and distribution.
What will happen to the github site itself? Not a whole lot. That's all pretty stable. More likely it will stagnate since they won't really know what to do with it.