This document lists all the planned deprecations.
The Handler
type and associated calls will be removed in version 2.0.
You should create your own implementation for handling OOP usage, but it's recommended to move away from using an OOP-style wrapper entirely.
The reason for this is that it's too easy for implementation details (for your application this is Flysystem) to leak into the application. The most important part for Flysystem is that it improves portability and creates a solid boundary between your application core and the infrastructure you use. The OOP-style handling breaks this principle, therefore I want to stop promoting it.