I'll be interested to follow this thread, as well.
It really comes down to ones needs and photographic wants.
For me, I shoot landscapes and stationary objects, mostly. Probably the biggest exception to that being my kids running around - although I get some missed shots there with my XTi, I have learned to work around the camera limitations and still get the shot.
I don't do almost any burst style shooting, except once in a blue moon.
I DO however like ultra wide angle with the occasional odd perspective from real low at an angle. In this case, sometimes even lying flat on the ground, it's kind of hard or impossible to see the viewfinder.
I also love night photography and go out early in the mornings before sunrise, still basically at night.
So I feel that the WiFi and Remote control live view without the need for a tethered laptop, router, or Eye-Fi cards would be awesome since I will be able to take shots with the 6D using my iPad as a live view controller which would allow me to compose a shot I otherwise wouldn't be able to compose.
Check this video out to see the remote app:
Also, the low light focusing - I am hoping this will help me with some of my night shots, as well, where the XTi is limited, hunts, and generally sucks. And, in those cases, I can barely see myself so even manual focus is very difficult as well. No one knows for sure how this will turn out, because no one owns a 6D yet; however, I am optimistic.
I am also probably one of 5 people who is really looking forward to the GPS. I love the idea of posting geotagged photos to Flickr since I like to notate where my shots were taken. I think this would be awesome for travel.
I did an 11 day photo tour of Iceland in 2008, and I would love to look at those photos now, 4.5 years later, and remember where the hell I shot each one of them on a map!
Plus, if I am going to shell out $1.5-$2k on a piece of electronics, I would rather spend the extra $500 and get one that is current (6D) vs. one that is 4 years old (5DII).
That's my situation and yours might be different, but these are some of the reasons I am eyeing the 6D as my next camera. I will still keep my XTi and my EF-S lenses and just add to my collection.