Im not sure exactly but i guess the extreme editions contain aspects of the technologies and features soon to be in the next generation to follow, the naming scheme might suggest this maybe.
Good question, would also like to know for sure
There's nothing fancy about the extreme edition chips at all. They're simply higher quality chips with fewer locked-out components and higher clock speeds.
The reason why the Sandybridge-E and Ivybridge-E chips are marketed as 3000 series and 4000 series processors respectively is because they are released within the same year as the Ivybridge and Haswell microprocessors respectively. This is the same reason behind rebranding the HD 7000 series GPUs as HD 8000 series GPUs, to make them look newer than they really are. It's marketing pure and simple.