I was browsing the script reference for the beta and came across this entry:
Are we intended to have this working in 5.6 or is this an artifact leftover from earlier work? I cannot actually change the API to .NET 4.6 and forum posts seem to indicate it won’t be ready any time soon, but I just wanted to be sure, as waiting on some of the features coming with the later versions of C# would greatly ease development for one of my potential projects.
The documentation here is a but confusing, sorry. In Unity 5.6, we are supporting .NET 4.6 for the Windows Store target only. That target does not use the Mono runtime, so we could more easily support .NET 4.6 with it for the .NET and IL2CPP scripting backends.
Support for .NET 4.6 in the editor and other platforms will be coming, but not in 5.6.