What I understood what you want to do is to use the new .csproj file format, and target any classic .NET framework, like .NET 4.5.2.
While the project itself works fine, you cannot choose "ADO.NET Entity Data Model" in the "Add New Item" dialog, forcing you to copy over an existing EDMX from a classic .csproj project.
And even after you did that, trying to change the EDMX in the designer and pressing Save just throws me a TargetInvocationException
every time, instead of updating the model.
Looking at the log file, the cause gets pretty clear: The designer is not capable of working with the new .csproj files.
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.InvalidOperationException: The "Content" rule is missing the "AutoGen" property.
at Microsoft.Verify.Operation(Boolean condition, String unformattedMessage, Object arg1, Object arg2)
at Microsoft.VisualStudio.ProjectSystem.VS.Implementation.PropertyPages.DynamicTypeBrowseObject.<<VSLangProj-FileProperties-get_IsCustomToolOutput>b__38_0>d.MoveNext()
So for now, you're out of luck if you want to keep using the designer.