While some cases are trivial, and MapReduce is pretty trivial, sharing is an integral part of doing most things practically applicable. In other words, the majority of real world applications of concurrency are hard.
I think that languages like Erlang, and many of the functional lanugages, show that you don't actually need shared ownership and shared mutation for a large proportion of the problems out there. (Shared constant values, of course, are not a problem.)
Linear typing can also help by enforcing ownership transfers between workers operating on data, allowing efficient data transfer without sharing.
