@gradyjenkins: WCF isn't part of core .NET itself and is a separate library so it wont ever be added to the core .NET standard API from my understanding. You may want to look into shared project for your apps.
@TamarinCodeMonkey: We are working on new project templates that will replace PCL with .NET Standard in a future release. The current flow is to upgrade via the flow I showed here. It is pretty simple to do, but will be default in the future.
@sabarinathan: Mobile Center makes it drop dead simple to build iOS and Android apps and has the benefit of using hosted Macs for both iOS and Android, so you don't have to worry about build machines. VSTS does offer a more powerful flow and control over the build, so if you are happy using VSTS it is fine to stay there. Under the hood Mobile Center is leveraging VSTS. There are some new steps in VSTS to submit your builds to the test and deploy section of Mobile Center that you may find useful.