I wish they targeted py3 from the beginning, by the time they get it usable to the mainstream developer (if...) py2 will be lagging a lot of features. That kinda sucks :/

Dropbox is py2 only (along with 80% of Python users as a whole). Business needs win out in this case.

If "business needs" was a real consideration, they'd just contribute to PyPy instead of writing a new implementation.

They have yet to present strong case for this project.

Could you explain why you think contributing to PyPy would better achieve the goal of replacing the Python implementation in Dropbox's codebase?

Because it's mature, fast and proven and has good comparability (Achilles hill: C extension support + numpy) , and it would benefit a lot from a high-profile contributor.

I suspect that Dropbox has a bunch of custom C extension code (Pyston puts C extension support as a high priority), which may have been a contributing factor here.