[glofish]

This is kind of a cop-out, how would anyone know?

Is Dropbox open source? Is Dropbox even a typical Python application representative of the challenges of porting from 2 to 3?

My hunch is that the challenges of porting Dropbox to any other language have to do less with Python more with the need to deal with a filesystem at a lower and more granular level than what typical programming languages offer. Thus everything needs to be rewritten in bazillions of ways to handle the bazillion corner cases.