Realised that the change in #77 also needed to be made to the .pp file.
Trying to test this, I realised that the UWP .pp files aren't even distributed, so spent a good while trying to get that to work. Eventually I came across this issue: NuGet/Home#1980 - which seems to mean that this isn't currently possible with the project.json UWP uses. Gaah. Will set up an issue to track that.
Anyway, to avoid completely wasting my time, thought I'd also push some of the other issues I encountered on the way. build.ps1 needed updating as the nuget.exe path for NuGet 3 has changed - so the nuspec with the contentFiles attribute couldn't be built. NuGet.config was added so we can pull in dev framework builds.
Update nuget features and uwp template
Looks good, thanks.