As you can see from the yellow alert box (shown above), changing to Disqus 2012 is now a permanent decision and once you do it, you can't change back. This note is now live on the Disqus 2012 FAQ page, at the very top.
The Disqus admin panel also shows a slightly new look towards the top, adding a link to the FAQ page. Take note that there's no longer an option anywhere to revert back.
Notice the link under "Disqus 2012". The appearance settings are still otherwise intact, and have not been changed as far as I know.
Personally, I see this as good and bad. I don't mind the change that much for this website, because generally everyone has been happy using the comments system based on the polling I've done, and so on. However for other users who aren't so "open" to Disqus might look at this as a slap in the face. I suggest that Disqus allows users to revert back. Why? -- well they did say that they weren't getting rid of the classic Disqus. This is an effort to get rid of it, basically going back on their word.
I like to see Disqus grow and innovate, but they did make a few promises that they were going to keep the classic Disqus. I haven't seen them make any type of public service announcement about this change, but if they did they didn't make it well known.
Honestly, if users complain about this I can't try to keep them at Disqus. They would have valid points.
Update: Okay, so I decided to send an email to Daniel Ha, the CEO and Cofounder of Disqus. He got back to me on a few words about this change, and that is below. Right now he hasn't spoken of a possible time frame.
We've carefully considered the usage behavior of Disqus and, after much polling and research, have decided to put more focus on delivering a single Disqus experience for websites. Older version of Disqus will eventually become unavailable.I also sent out a tweet before I emailed Daniel about this, and one of their support members got back to me as well.
@the_mhazell Most site's are switching regardless and we're unable to support the Classic version forever. -Talton
— DISQUS Help (@disqushelp) February 1, 2013