From some threads here on MPGH, as well as articles over the internet, I have seen either "Yes, there will be a MW3" or "No, there will not be a MW3".
From what I see, here are some reasons why I hope there will be another MW.
-Makarov was never found.
-When Nikolai rescues Soap and Price, he says "They'll be looking for us you know, I know a place.."
-At the end of Whiskey Hotel, they mention "going to Moscow".