Not yet, but I have it on my watchlist. I wait for wider (rust-like) adoption of Nim, because most of my programming tasks are heavily dependent on the ecosystem and requires a fair amount of libraries.
Also, the FFI in Nim is basically just declaring some C function as a `proc`. So, wrapping existing C libraries is as easy as Cython for Python. You can even jump start things by running `c2nim` on a header file.
I know there are a few different protobuf impls floating around. Not sure how much google pubsub needs beyond that. It's probably not so far away. Maybe you can be the one to do the pubsub wrapper. :-) (I'm only trying to encourage, not enlist/conscript.)