If they were doing terrain specific stormtroopers, Why are the heavy stormtroopers not sandtroopers? Instead they have no environmental specialization and just a larger weapon.
Also we don't have any existing snow tiles. While yes, they could create a large number of snow tiles to represent the first act of one movie, it is more cost effective and logical for fantasy flight to supplement the existing, and far more adaptable to any planet, jungle and sand terrain. Now depending on how many tiles are in the new expansion box, it could happen.
Sculpting a new miniature to represent a snow trooper is also an extra cost. We see them once. Even the AT-AT shows up on Endor. The cons outweigh the pros for making a miniature. For a figure that is a Stormtrooper for all intents and purposes, but has a cold environment tag is not as useful overall, especially in skirmish, if the rebels don't have similar figures.
Now if Fantasy Flight made a full size 100 dollar new campaign box that was all about Hoth, with 9 scrubbing bubble troopers amongst others and a whole box full of open white terrain tiles then that is fine. But for the mini expansion that twin Suns is, with seemingly 10 figures, two being new heroes, I don't see specialized imperial troops, being produced. At least for a while.
As of now, fantasy flight is giving us, apart from the tuskans, figures that are useful in any setting and look like the basic Stormtrooper.
Cost wise sculpting new units that have vastly different capabilities is a better bet, such as scout troopers or TIE pilots as they can be used in more scenarios then cold weather attack troops.
I think this conversations has got confused at some point. I was not suggesting they would make Snow Troopers, I was suggesting that they could very well release a Hoth pack with new Stormtroopers that are NOT Snow Troopers, a possibility you yourself seem to be advocating with the example of Heavy Troopers. I don't understand why you see this as an argument against a Hoth pack, any more than it is against a Tatooine pack.