The 3.0 version of the MPI standard formally deleted the C++ interface (it was previously deprecated). While implementations may still support it, features that are new in MPI-3 do not have a C++ interface defined in the MPI standard. See http://blogs.cisco.com/performance/the-mpi-c-bindings-what-happened-and-why/ for more information.
The motivation for removing the C++ interface from MPI was that it had no significant value over the C interface. There were very few differences other than "s/_/::/g" and many features that C++ users are accustomed to were not employed (e.g. automatic type determination via templates).
As someone who participates in the MPI Forum and works with a number of C++ projects that have implemented their own C++ interface to the MPI C functions, I would like to know what are the desirable features of a C++ interface to MPI. While I commit to nothing, I would be interested in seeing the implementation of a standalone MPI C++ interface that meets the needs of many users.
And yes, I am familiar with Boost::MPI (http://www.boost.org/doc/libs/1_54_0/doc/html/mpi.html) but it only supports MPI-1 features and the serialization model would be extremely difficult to support for RMA.
One C++ interface to MPI that I like is that of Elemental (https://github.com/poulson/Elemental/blob/master/src/core/imports/mpi.cpp) so perhaps people can provide some pro and con w.r.t. that approach. In particular, I think MpiMap solves an essential problem.