The last co-operative third-person shooter IO Interactive developed was the divisive Kane & Lynch 2: Dog Days.
Despite taking a bit of a critical pounding, the game sold exceptionally well on the back of its unique visual style. So it wouldn't be a surprise if we did see another title in the series.
And in a recent job listing for a senior programmer, the company has hinted at just that — seeking employees to work on an "unannounced 3rd person game with strong cooperative multiplayer elements".
Sounds like Kane & Lynch to us. Hopefully there's less nude shootouts this time around.