Just spoke to the people at Zipp and found out some interesting info...

The conversion from 10 speed to 11 will cost $250.00 through Zipp. It is only going to be offered for 2012 wheels. I thought it was interesting that they cut it off 2012, and did not include the entire FC line up. It might be wise to sell your current FC rears if you plan on going to 11 speed in the future.

I would guess that other companies might do the conversion on earlier wheels, but total speculation on my part.

Here is the link...

http://www.zipp.com/about/story.php?ID=496