Yeah, that would be my recommendation.
We’ve recently introduced a new system for ‘plugin modifiers’, which are super cheap extension points which are similar to DiscourseEvent but they take an input value and return a value. So in your case, you could make a core PR to add a DiscoursePluginRegistry.apply_modifier call in the relevant include_ method, and then you can use register_modifier in your plugin to override the value.
It’s likely we’ll eventually block it completely, yes. Plus you really don’t want to be using a method that’s printing deprecation noise in the logs.
If you really must override a method without co-operation from core, then modify_class would seem to be the better choice. The main reason we have a dedicated add_to_serializer is because it auto-defines an include_* method so that it only applies when the plugin is enabled.
That means that the code snippet you linked is currently defining two methods. include_wizard_required? and include_include_wizard_required? 