Is .NET CLI only for .NET Core?

You can use dotnet cli for full framework apps and libraries as well. You just need to use the appropriate framework tag - for example "net46" to target .NET 4.6. You can target multiple frameworks, too:

For example, from my Noda Time library:

"frameworks": {
  "net45": {
    "frameworkAssemblies": {
      "System.Xml": "",
      "System.Numerics": ""
    }
  },
  "netstandard1.1": {
    "buildOptions": {
      "define": [ "PCL" ]
    },
    "dependencies": {
      "System.Diagnostics.Debug": "4.0.11",
      "System.Globalization": "4.0.11",
      "System.Linq": "4.1.0",
      "System.Resources.ResourceManager": "4.0.1",
      "System.Runtime.Extensions": "4.1.0",
      "System.Runtime.Numerics": "4.0.1",
      "System.Runtime.Serialization.Xml": "4.1.1",
      "System.Threading": "4.0.11",
      "System.Xml.XmlSerializer": "4.0.11"
    }
  }
}

The PCL preprocessor symbol will be renamed to "DOTNET_CORE" or similar at some point - it's only there because I have a bunch of code that uses it for conditional compilation back when I used to target portable class libraries.

You can still also target portable class libraries, by the way... so a single package can target many different versions.