I'd be happy to see an FFG AT-AT model regardless of how they integrate it into the game...providing they stay far, far away from the "sliding scale" concept they've used in X-Wing and Armada. There are multiple options out there already if someone wants a "meh, it's taller than an AT-ST, close enough" model - most of them substantially cheaper than any FFG version could end up being no matter how compromised the scale - and a grand total of zero options if you want one that's "correct".
That said, it's not something that would likely do well in regular play, you'd have to design scenarios around it - but that's doable. There was a great fun scenario for GorkaMorka that featured "rolling terrain", ie you picked "front" and "back" edges to establish a direction of travel, and every turn all the terrain shifted a given number of inches towards the "back" edge, with "new" terrain being randomly placed at the "front" edge. Something similar could work for an AT-AT, make it a "fixed" feature around which the terrain shifts.