Merrick here...

CHRIS PINE.

He'd been widely conjectured to be the man, and was identified last week by Hollywood Reporter as being in talks for the role.

But there was some question about his casting...he'd also been offered a role in a new Joe Carnahan movie called WHITE JAZZ, whose filming conflicted with JJ's TREK.

Something had to give.

And, it seems the issue has now been resolved - per this posting on Joe Carnahan's blog:

Kids:

The young man playing Junior Stemmons has opted to 'boldly go where no man
has gone before' and thus, had to bow out of WHITE JAZZ. I've been talking
to him this past week and knew how tough the decision had to be for him.
I don't envy ever being in that spot but I gave him my full support, even if
it meant he didn't do JAZZ. I get it. You don't get opportunities like that
often and I told him as long as he could control as much of that process as
possible and not get sucked into doing lesser sequels as a result of taking
this gig, then good luck and God bless.

We're sure to do something down the road. I've already slotted him in for
KILLING PABLO.

JC

Must've been a difficult decision for Pine; he has some big, flamboyant footsteps to follow.