I would say that VC is unlikely to ever support all the libraries one might want to use, because any C modules need to both support the stackless Python and be compiled with the correct toolchain to work. The Python in VC is really meant just for simulation configuration and implementing simulation logic, its not a general-purpose Python environment in that sense.
If you only need to do “offline” analysis of data, i.e. the results aren’t needed during simulation, using external environment for that should be pretty straight-forward. You can write files from VC Python scripts and use e.g. Pickle to serialize your data. It should be also possible to run shell commands from VC Python so you could e.g. trigger your external Python 3 code automatically and read results back to VC if needed. This way your data transfer and analysis execution can be fully automatic.
With external environment you of course gain the comforts of advanced IDEs, package managers, debugging etc. so it can be easier and faster to develop your analysis there anyway.