Looking the picture over, I see a couple things...
-First there's a large hatch running along what I assume will be a lower level, just like all diagrams basically show of the AT-AT, and which the models have. That's obviously new, as is the ass-hatch which does appear to be open... I would say, assuming that lower hatch is figure-sized for the most part in terms of height, that the body's about 1.5 to 2 times the size of the old body of an AT-AT then.
This is assuming there's space there to get your hands in and put figures, etc.
-The head is probably what I consider the letdown... It looks stumpy, like the old one, and something just seems off about it. The guns I'm wagering will have realistic versions you can replace, much like the AT-ST did, for the cheeks... The head's clearly new and larger in sculpt, but it doesn't look like it necessarilly fits 6 figures properly (IE: Standing). There's just something off about it. It's the most glaring issue I see.
-The entire torso/body's sporting the cheaper "single-mold" style that the AT-TE and BMFalcon had too... Notice how details all sort of sink together, but aren't separate. It's basically a couple large single pieces that'll get screwed together. The color of the plastic used (assuming it's not the final color since AT-AT's aren't white) doesn't do justice to it, so it may look better molded in grey... I dare say the original AT-AT had some sharper sculpt to it.
-If the body's bigger, which I'm assuming it is by my guesses on that troop door, the legs are larger as well, but it's tough to tell how much larger/longer they are.
I do believe this is the upcoming AT-AT. There's way too much new there I think for it to not be, and it's about what I was expecting. Kind of an "up-sizing" of the original more than something completely redesigned from the drawing board. Some folks will be happy with that I think, and others won't, and that's fine. I didn't plan on buying the new AT-AT because it's not to-scale so it's out of my buying realm... Though 3 feet (if it comes to that) isn't all that bad really, in the scale world.
And I find the Speederbike garage in the ass to be very lame. Speederbikes are tiny, and they actually fit in racks and things in the rear section with doors that open on the side. Having some mechanics of the walker actually flip open as a door is meh to me. I felt the same way about the BARC in the TurboTank's supposed area of the drive section for the wheels and stuff. It's a play feature, but it's sucking up interior space, so I'm not fond of that I guess (Maybe the better analogy is the little escape thing on the BMF. I didn't care for that either and would rather had another section of the Falcon's interior I think).