We don't have roadmaps or a prioritized backlog, so we weren't exactly "waiting" to implement this. Someone got fed up with the image workflow, figured out a solution, grabbed some other people to help, and shipped it.
I imagine the conversation internally went something like, "Man, attaching an image to an issue is really annoying. Let's make it not suck." An issue and pull request followed, internally shipped it to test it, and today rolled it out to you all.
That's literally how 99.99% of features happen on GitHub. :)
This is good enough for me :)