While looking up some stuff in the book “Integration Patterns” I spotted a tiny sentence that is amazingly close to REST. In chapter one on page 3 the authors (among them Gregor Hohpe, BTW) emphasize that from the point of view of integration the whole must be considered instead of solely designing for each integration between two applications in turn. The sentence is
However, if you approach this same problem from an integration architecture perspective, the ideal application is a thin layer of presentation that consumes shared functionality or data at the enterprise level.
I find this amazingly close to the notion of a user agent component consuming representations and capabilities provided by resources.