[This email will arrive approx 15 hours after I’ve written it. Sorry if there’s been talk on this post by that stage that I am “ignoring”]
I’m not sure I can agree with such a feature being a part of Rails just yet. There is currently many different approaches to designing APIs with Rails, going from the very basic “render JSON” calls in the controllers, to rabl and (god forbid, only because the syntax is really ugly) JBuilder, to ActiveModel::Serializers and not to forget the new Rails::API gem thing that Santiago Pastorino and co are working on.
My point is that there’s all these different ways to do the design of the API and, besides the default render call, none of these are core Rails features. They’re all external gems that offer their unique take on how to “properly” design an API.
I can definitely see how, in a very small use case, versioning the views for an API could be useful. In my experience, however, it’s usually more than just the view that changes between versions. The controller receives customizations as well, sometimes. Therefore, I think that versioning the views is not a “majority case” and shouldn’t be a core feature.
I think the best course of action here is to leave the functionality as a gem and promote it as yet another alternative to designing an API with Rails.