It's almost certainly to be a follow-on to MW2 based on the official sources gathered over the past 6 months. The only debate is whether it's gonna be a DLC like originally intended, a standalone spin-off, or Modern Warfare 3. It honestly wouldn't surprise me if they still haven't decided this yet. I can't see it being presented as DLC or an expansion though because of the state MW2 is currently in. A spin-off could be a nice alternative especially under new developers but it may be seen as a weak move for driving sales. MW3 it may turn out to be if Activision just want to wind up and conclude the trilogy early rather have yet another IW effort released within the next two years.
I'm really not holding out much hope but still interested to see what SHG do as they always try their best despite being heavily under-resourced compared to the other studios and having huge personnel turnover. I'm not hyped in the slightest though and if someone said to me you can never play another COD game ever, I would not give a toss.