There may be no Men in Black 4; Will Smith isn't keen. And he's right too. These things are better left at no.3, especially if they start to go downhill.
That's not to say the franchise won't continue without him but let's be honest here, he's pretty much the only reason we'd watch those movies in the first place. Will Sony continue and bring in a new head honcho (they confirmed earlier in the year that they'd green-lighted the fourth film)?
In an interview with Collider, Smith said: "I think three is enough for me," Smith said. "Three of anything is enough for me. We'll look at it and we'll consider it, but it feels like it might be time to let someone else do that."
You're shpot on, Will; but what you really SHOULD consider is more dancing and rapping on Graham Norton, 'cause that was all kinds of awesome.