Asked this question on Rails core google group. Got some answers, nothing definitive. (see response). Anyone working on it? If not, I’ll provide an initial draft.
I believe that you’re on the right track with your model decorator idea and the same can be applied to controllers as well. Do that.
Before I start writing, I think it would be edit the http://edgeguides.rubyonrails.org/engines.html#improving-engine-functionality to describe extending Rails Engines by explaining,
- how to add methods to existing engine models/controllers
- how to override methods of existing engine models/controllers
- how to use ActiveSupport::Concern to structure Engine models/controllers Concur?
Gosh, I feel like this is growing into a book.
Yes, I agree with these things.
A book about engines has crossed my mind more than once 