The plugin for NativeScript for Visual Studio support (mentioned here) is part of AppBuilder, which is not inherently free. There is no documentation that really explains whether a license for AppBuilder is required to use it, or if that also supports open source.
Does anybody know if the plugin mentioned in the link above is supported?
The Telerik Platform (which includes AppBuilder) tools and services are paid, but come with a 30 day free trial. And yes this is the case if you are developing with NativeScript or Cordova.
If you want to go 100% free, you can use the NativeScript CLI.