Dragon is not known for their accuracy, among military modellers. They should have 3d scanned the ILM model, if any of them still exist. They used reference books, which is good, however ILM made many different AT-ATs for different shots, so they're all slightly different. I've noticed they don't have articulated ankles, this will be impossible to pose in a walking position, accurately, without it looking the way it does in the photos. However, I can say its leaps and bounds better than the 36 year old 1/100 MPC/AMT kit. That thing, by today's standards is terrible.
As far as the scale its hard to say, because there's no reference point, other than the figures I assume are 1/144. Wookieepedia says an AT-AT is 22.5m, so 1/144 would be 6.15". Looks small compared to the TIE in the background, that is also supposed to be 1/144. We'll see when they actually market the product, I figure these are pre-production prototypes.
If they can stay under the $50 mark, and they are indeed 6" tall. I'm in. Dragon kits are expensive, they make quality kits, plus the Star Wars licencing, I can only guess as to the price.