为什么我的project.json / xproj项目没有在Visual Studio 15（预览版）中打开？

I have an existing solution involving multiple project.json (and corresponding xproj) projects that I have been working on for some time. It works fine in Visual Studio 2015, but it fails to load in VS 15 (preview), just showing a failed load icon for each. No messages are printed. I have an existing solution involving multiple