Sorry, but this one reeks of made-up publicity / anything for a headline:

Director Barry Sonnenfeld revealed Will came up with the idea himself…

He said: “Will calls me Baz. When we were shooting ‘Men In Black II’ [in 2002], one night he said ‘Hey Baz, I think I have an idea for number three’. The basic idea was that Will’s character, Agent J, would have to go back into the past to save his partner.

“It allowed the movie to take place in another era, and us to learn more about Tommy Lee Jones’ character. But it turned out to be a very long process of development, mainly because of the knotting issues of time travel, the time travel thing was really hard.”

Could be true. Even it it was, as Sonnenfeld pointed out, time travel is a tricky topic when it comes to story-telling. It’s continuity cubed. Simply voicing the idea isn’t the same as writing the script. And of course, the MIB franchise has always had a 50s/60s feel to it, just like the Blues Brothers did.