Pre-orders are up at TFSource! Looks like there will be two versions. And, excitingly, looks like it beats the TFC version, coming in at $82.99!
US VersionJapanese VersionThe difference appears to be the arm color, which explains why some of the pics we've seen previously had red arms and others had black arms.
There's some new pics, including the placement of the tower. (Looks like it is my second guess, of those screw holes.)

Slammer's tank mode:

What the red guns look like:

So I put in my pre-order! Even though I have the U.S. Metroplex, I ordered the "Japanese" version of this guy. I like the red arms better, they'll provide a better contrast against the black guns when you have those attached.
Anyway, I am loving this Sixgun. Looks like the parts are well utilized. And, unlike TFC's version, he's quite like his G1 self in that he is made from six guns! (The two that make his legs, the twin guns on his back, and using the two black guns that come with Metroplex on his arms.)
And, of course, the fact that it comes with Slammer, as well! So with this, and the fact that Metroplex already came with Scamper, and you'll have the complete Metroplex team!