Assassinator just mentioned this to me.
Seems that Youtube upped their max resolution a few weeks back.
It now allows 4096x2304 resolution (9.4 megapixels) videos, which is a bit larger than QuadHD (3840x2160).  Too bad it's only being fuelled by a 6Mbps nominal bitrate (from what I've read), which is probably better suited to 1920x1080 content (and in fact, may not be enough for some 1080p sources).

Of course, there's potentially many problems with this:

• Who has such a large monitor?
  
• What video content comes in that resolution?  There's very little *true* 1080p content out there, so what's the chance of 2304p?  Only reliable source I can think of is gaming/CG, but these will absolutely rape the 6Mbps bitrate, and 720p @2Mbps probably will look heaps better.
  
• IMAX projectors run at 2k resolution
  
• Many CPUs can't decode it without lag (especially going to slow Flash); I suspect it will choke all but the best Core 2's, but I can't seem to find reliable results
  
• DXVA (GPU decoding) probably chokes on it too.
  
• I guess faster connections are becoming more commonplace, so 6Mbps probably isn't too hard to stream in some parts of the world
  

So, just a game to get the bigger e-peen?