There are numerous benchmarks implemented in Chapel, some of which are competitive with other implementations (see paper reference in article). There is a growing standard library and literally thousands of test codes that represent a broad set of functionality. That said, Chapel is not yet a product grade language, nor is it promoted as such.
Chapel may not be an appropriate replacement for all MPI programs, but it can be used for some programs today.
I agree with this, but it also sort of risks being a self-fulfilling prophesy; everyone uses MPI because everyone uses MPI, and no one uses Chapel yet because no one uses Chapel yet. At some point, we who are willing to be early adopters need to just start.
Chapel may not be an appropriate replacement for all MPI programs, but it can be used for some programs today.