Python isn't going anywhere. No other language has such a rich set of tools for the complete analytic workflow from data acquisition and transformation, through analysis to end product creation (i.e. web/application development). I think in terms of an exploratory/prototyping language it is going to be at the top of the heap for a long time.

Julia is an extremely interesting language, in some ways it is more "pythonic" than Python (at least in regards to consistency), while also being surprisingly lisp-like. Unfortunately, the library ecosystem is still extremely immature. Within ten or fifteen years, I expect Julia will take over pretty much all of Python's niches.

As for systems/backend code, I'd bet on Scala over go; much more interesting language, and able to leverage the massive java ecosystem.