It is very unlikely that you will ever see this on a Pro Tour (or whatever it's called these days) level bike. But the reality is that this marks a more important milestone than the it's big brother launch last year. Of course we all lust over the top end groupset, but the fact is that Ultegra is within reach for more people.

Details are very vague at the moment, but one thing we can expect is that the cables will be hidden under the tape just like 7900 Dura Ace. What is unknown is if 6700 will be closer to the 6600 SL or standard 6600. For anyone who had chance to use 6600 SL, it was difficult not to justify the extra expense of 7800. The most important tactile area for me on a groupset is how the shifter feels in use. This is a constant variable no matter what size bike or weight the rider is. Braking can differ depending on the size of the bike and pilot.

Rumours are that the Rabobank Team have been testing it for Shimano to offer valuable rider feedback. As they have a Pro Continental Team also, it may appear on one of these bikes at a race near you.
I am expecting evolution and not revolution, Shimano don't normally make bold moves and prefer to have a system that works without fault. So I'll have a go with predictions:

Shifters - still alloy, but under the bar.
Chainset - this will in effect be 7800 rebranded
Front mech - stiffer more precise than before
Rear mech - this may be one area to get the carbon treatment
Cassette - I wouldn't be shocked if we see something with more than a nod to Sram Red offering
I am sure that it is due for a Fall launch and expect to see it everywhere come Eurobike.