Can't speak for the parent but having tackled similar efforts before I find that almost all APIs regardless of the implementation flavor (including SOAP and RPC) are readily understood as CRUD systems creating/reading/updating/deleting things), and the mapping from CRUD to REST is straightforward. In practice this generally means mapping from a SOAP call like `SetPostAuthor` to a REST call like `PUT /post/:post_id/author`. There are always some gnarly bits along the way, but the basic structure usually comes together pretty easily.

Yup, petty much. If you're willing to be a little flexible in your application of RESTful concepts and are okay with your abstractions leaking a bit, it's not especially tough.

That's the easy case.

A harder case is when you have a "service" layer which also has a large collection of queries at various levels of abstraction.

These map poorly into resources, where you want a single level of abstraction per resource. And they map badly to legacy consumers, who've grown comfortable to having a collection of special knobs and dials perfectly shaped for their exact needs.