On the topic of large companies still using Python 2, I would love to hear about Splunk's upgrade plans. They have the following[1] on their SDK page about upgrading, but my understanding is their entire platform is still on Python 2.
I've upgraded a number of projects at my work to Python 3 this year, but nothing that 2-3 developers couldn't do in a few weeks. Can only imagine the headache of migrating something the size of Splunk.