Though the argument is that because all of the innovation is happening in .NET Core (and indeed the .NET Standard 1.x versions were a game of .NET Core implementing things first and backports eventually made to .NET Framework), the clear indicator seems to be that .NET Core is the present-future platform (ie, the "current iteration") for .NET and .NET Framework the backwards-compatible past. Though Microsoft has walked that messaging back, somewhat, it's very much the case that greenfield projects today are best on .NET Core, and even brownfield projects are welcome on .NET Core (.NET Core 3.0 "Desktop Pack" is now the best way to build and run WinForms and WPF applications).