At the time of writing this article, Alpine Day has finished and Alpine 3.x has only been out a few hours. The new documentation states that components powered by Alpine.data declarations that contain an init function will automatically have the init function called. This is great and saves you some time since you don't need to hook up the x-init directive. After reading through the source code, it turns out you can actually add an init function to any data object and Alpine will still call that function automatically.
This is something that Spruce supported to, so if you used that with Alpine 2.x you'll be familiar with this one.