have been discussing the next steps with a twitter engineer working on integrating it with an ipython wrapper we have internally, and the speedup alone from v2 is huge, but we're considering either hacks to pex or hacks to our ipython wrapper to support incrementally loading new packages into the running environment

If modifying PEX is the route you choose, please 1st consider the existing

PYTHONPATH

+

PEX_INHERIT_PATH=prefer

support 1st. Pants aside, setting up a side-car dir as the preferred mutable site-packages dir for a running pex would seem to work given just Pex.

that's about what @rough-minister-58256 was thinking (or at least, we discussed symlinks and chroots a bit as an optimization)!