I don't think Python would have succeeded as a language if they hadn't done Python 3.

I assumed Python 2 was pretty much ubiquitous and that the world wasn't adopting Python 3 very quickly for a long time, but I do wonder if the applications I was working with a decade and a half ago (ArcGIS, Blender, Civ4, lots of Red Hat system tools, etc.) biased that viewpoint.