.net 4.6.2: "Long Path Support (MAXPATH) - We fixed the 260 character (MAXPATH) file name length limitation in the System.IO APIs."
https://blogs.msdn.microsoft.com/dotnet/2016/08/02/announcing-net-framework-4-6-2/?MC=Windows&MC...
Seems to be available in Win 10 anniversary update (with a group policy setting)
Recent builds of Powershell +.net4.6.2 should have this change enabled. That may include WMF 5.1 preview (I'm not sure).
How it works on older versions of windows is less certain.
I think lots more reading of Jeremy Kuhne's blog entries is needed.
https://blogs.msdn.microsoft.com/jeremykuhne/2016/07/30/net-4-6-2-and-long-paths-on-windows-10/
offline installer: https://www.microsoft.com/en-us/download/details.aspx?id=53344
Figured I'd throw this up here as I've not seen it mentioned yet.