I'd love to see a feature where, when I come to the ES docs pages, it would remember which version of the docs I looked at last and tried to use that version. I often come to the docs through Google but almost always to the 1.4 or 1.6 docs, read a bit, go "huh? I thought they changed that" and then remember that I have to select the right version 
Thanks!
Thanks for the feedback, I have raised this with our website team to see what we could do.
One potential problem I can see coming up is that I'm not sure how we would distinguish between a user just going to the documentation and the user explicitly wanting a particular version since the version is in the URL that you navigate to.
I hear what you say. A solution for that of the top of my head: if a version cookie is detected go to version in cookie. In case of an explicit switch, add an extra URL param (something like switch_version=true) to signal to the code that the cookie should be rewritten with this new version. I have all the confidence that you might come up with a more elegant solution