Unity 8 will offer the traditional desktop interface when it detects a desktop. The same OS will switch to a touch-based interface on touch-based devices such as tablets and smartphones.
As a smaller and cross-platform subset of the .NET Framework, it will have its own update schedule, updating multiple times a year, while .NET will be updated once a year. At the release of .NET 4.6, Core will be a clear subset of the .NET Framework. With future iterations it will be ahead of the .NET Framework. "The .NET Core platform is a new .NET stack that is optimized for open source development and agile delivery on NuGet. We're working with the Mono community to make it great on Windows, Linux and Mac, and Microsoft will support it on all three platforms."