I haven't checked on Julia for like a year, but back then Julia didn't offer anything above and beyond R when it comes to "big" (really just not fitting into memory) data. As it is Spark with Scala is both faster and more convenient than R or Julia.
Spark has a python API and python has a bigger ecosystem for exploratory data analysis than spark.
Also python has a big data interface with out of core matrices and tables as well as a compiler than can speed numerical code, with a just a function decorator, to C like speeds. The former is an interface to the latter.
