JSON in HTTP GET/POST. It's more of a nuisance, but it forces you to face the network issues head-on, and code that reads JSON can't afford to make assumptions, so it ends up less brittle.
To be honest, I like REST for CRUD of things that are natural resources, but I think it's wasted extra work for operations that are natural RPCs.
The "nuisance" of JSON+HTTP is a backward step in a way, but it lets you solve those problems. Sounds like an ideal solution would be an abstraction with less nuisance, that solves the network issues that it can and gives you access for the others - which may or may not be possible; it's an ideal.
(1) By "network issues" do you mean along the lines of Peter Deutsch's "8 Fallacies of Distributed Computing"? http://en.wikipedia.org/wiki/Fallacies_of_Distributed_Comput...
(2) Regarding "assumptions" and "less brittle", do you mean issues of reading the format correctly, in the face of evolution of the internal structure and/or wire format?