The book description on the product page for 2312 discusses the mercurial city of Terminator which plays a key role in Blue Mars. I find it doubtful that this upcoming book WON'T draw from KSR's other novels. I expect that we might even see some character cameos.
Having finished the novel, I can confirm that book does NOT take place in the same continuity. There are some similarities (such as Terminator, the Accelerando being mentioned and a few other elements), but also several radical differences. Most notably, the colonisation happens a lot later (in the 2060s), the Chinese are involved (which they weren't in the original trilogy) and there's only one revolution, not several.
I tend to have thought any differences were mainly cosmetic. For example the Chinese thing is merely a modern interpretation on China obviously currently being a bigger power now than when the Mars trilogy was written, likewise the former soviet countries have lost a lot of what they had then. The later colonisation so perhaps people take 2312 seriously (cause we are supposed to be sending 100 people there in under 15 years time!!!) Things such as the 'Accellerando', longevity treatments, the song saying something about 'floating about like Peter', Terminator, the Martian and solar system political system, Soletta, the AI's name being Pauline (which was also coincidently Boone's AI name). Other things too. Too many similarities in my opinion to say that its definately NOT in the same universe. You could also go on and theorise other links (In my mind the main character is a distant relative of Hiroko :). In the end I read it as though it was the same universe and didnt find it to be an issue. Remember it is set 100 years after Blue Mars ended, and while I can agree that the setting is more likely to do with being 300 years from now, in 100 years a lot can happen, as we saw in the MT.