I just noticed that when I watched this video in Chrome (and only Chrome), that the video now has an option for 2D or 3D anaglyph (only 3D option).
I then disabled the HTML5 player to revert back to the Flash-based player and confirmed that the above was really appearing in the HTML5 player, not flash.
Unfortunately, this new HTML5 3D video capability appears solely in Chrome. It did not appear in Firefox, Opera or Internet Explorer when I tested each.
Having just watched The Martian (in 3D) at the theater today, it reaffirmed for us that we really like 3D! Let’s hope that Google is able to bring back more 3D viewing options to Youtube soon!