It is 2018 and I am all in on Multi-Target projects for building libraries and plugins. I love them so much that I convinced Frank to record a full episode of Merge Conflict on why this whole thing is so absolutely amazing.
I have slowly been converting all of my plugins over to mutli-targeted projects, which has reduced some of the solutions from 15 project down to 1!!!
There is a bit of tiny setup required for multi-targeting and for it to automatically pump out the NuGet package for you, which is why I updated my Plugin for Xamarin Templates for Visual Studio 2017! It handles everything for you automatically :)
Not only great for Plugins, but any cross-platform library!
Here is a full walkthrough of exactly how they work: