When it comes to scale in this line, I've just accepted that your odds are low of getting anything "accurate". Not to say it doesn't happen, it does more than people realize, but I think it's more a fluke when it does happen than something intentional.
The AT-AT is project I've had for years now... 40"-ish high (rounded) is about where you'd be for scale, and a little longer than that. I'd love it, but I don't expect it ever.
For me I'd like to see a scale AT-ST (in the feasible range of resculpts) first. It's got to be the most inaccurately sculpted vintage vehicle they still crank the molds out for, and to get one in perfect scale to the figures wouldn't be difficult. This is the single vehicle I think I'd like to see resculpted from the OT at this point... The Snowspeeder is a close runner-up though (I'm not counting the Speederbike, I think they'll give it a go sometime).