When you access a database with FileMaker Go, it doesn't magically turn into a mobile app. It might look like an app, but it's really just a database. FileMaker Go is the app.
If you've ever spoken with a customer who is interested in having a mobile app developed, then you know how challenging it can be to pitch a FileMaker-based solution. They're surprised when you tell them that their users will need FileMaker Go. If their users will need to connect to a hosted database, then costly Concurrent Connections will be required - and that will surprise the customer as well. But it's when you explain to them that they won't be able to sell these "apps" on the App Store that the opportunity will quickly fade away - especially if that's the customer's ultimate goal.
FileMaker is a platform for developing custom database solutions. It's not a tool for developing apps.
If you are interested in developing native desktop, mobile, and Web applications - apps that don't require costly licenses and that you can sell on the App Store - then I encourage you to take a look at Xojo. Xojo is a multi-platform development tool that you can use to create native desktop (OS X, Windows, and Linux), Web, mobile (iOS), and even Raspberry Pi apps. Xojo's licensing model is developer-friendly. You only need to purchase annual development licenses for the platforms that you want to build for. No end user licenses or concurrent connections are required.
Also, I invite you to join fellow FileMaker / Xojo developer Hal Gumbert and I for "Xojo Q&A for FileMaker Developers." It's a free webinar hosted by Xojo Developer Evangelist Paul Lefebvre, and Hal and I will be panelists. We'll discuss Xojo from the perspective of FileMaker developers, share techniques for integrating Xojo-based apps with FileMaker databases, answer your questions, and more.
The webinar is being held on December 8th at 11:00 AM Eastern Time. Click here to signup.