I think the author nailed it. This is Microsoft's chance to reach out to developers and prove that they've had a change of heart regarding open source. We've seen this over the years with previous code hosting platforms. If the platforms betrays it's users, developers are not scared to mass migrate to something else. The onus is now on Microsoft to keep developers happy or risk losing their $7.5B investment.
That to me is what DotNet Core is, along with Asp.Net, Entity Framework many years ago, and everything developer related becoming open source. GitHub is just a signal to people who have been out of the loop, bloomberg and many linux developers. When I start dropping my apps on their systems, they might be surprised how well they run. https://github.com/dotnet https://github.com/aspnet
DotNet Core debugger is proprietary . You can only debug apps within Microsoft environment according to their license.
Same thing for most of the azure tools , you are only allowed to use them within Visual Studio.
I don't really called that "all in open source" .
It's gimmick to give C# devs the illusion of a choice.
Try to build , run & deploy a C# app on AWS with Atom. You're gonna have a bad time.