What's next?

From the Eurogamer comments thread on the news that Call of Duty 4 sold very well.

COD4 isn't revolutionary in any way. And I just hate franchises that release new installments every year. COD is turning into something like FIFA. What's next, COD8, COD11...?

I would imagine CoD 5 is next. Just a wild stab in the dark, like.