Lots of finance companies shell out a lot of money for KDB+, a fast real-time database. Other than performance, the main selling point is that it comes with its own imperative language (K/Q). You can build entire API's and trading systems in Q: persistence, load balancing, streaming analytics, &tc. In that way, Q solves a different "two-language problem". There are not many serious competitors.

If Julia had its own lean realtime database implementation, then I can see it becomming a killer language for finance. JuliaDB/OnlineStats is probably 60% of the way there.

FWIW: I am using it as a general purpose language at the intersection of large data sets, analytics, and related bits. At a prop shop.

YMMV, but I find it is fantastic in this use case. And I don't have to worry about semantic space.