This decoupling of commands from effects is interesting, but I don't think I'd use it in most places. In this specific example, passing in an interface for an API client (or whatever other thing you want to call) lets you create a mock client and pass that in during testing, and different environments should be configured differently anyway.

There is one place I'd consider this though, and it's incredibly specific: a MTG rules engine. Because of replacement effects, triggered abilities, and so on, being able to intercept everything from starting turns to taking damage means you can apply the various different game effects when they come up rather than mixing that logic up all over the codebase. I'm tempted to try this and see if it works, actually.