The following response comes from Treyarch community manager Josh Olin after being asked about the possibility of a direct sequel to Call of Duty: Black Ops.
“Your guess is as good as mine. We’re so happy with Black Ops - it was incredible. Everyone hoped it would have this kind of success. We all knew how well MW2 did [in 2009], breaking all entertainment records, so the fact that Black Ops broke through it for a second year in a row and reset that record was incredible. We’re still really glad that we hit the ground with the DLC when we finished the game, because we knew we wanted to get it back out there.”
I think a direct sequel is pretty likely, but it’ll be a few years. Being the best-selling Call of Duty game yet, a direct sequel seems like a no-brainer to me.