I'd like to think Sierra Nevada and the work that PaZzmod has done is what prompt the ATS rebuilds. If I had to say dlc's though, I'd go with Idaho and Utah. Idaho hit the mark visually on what the standards should be. Utah hit the stand for rock formations. Both have taken off with Colorado and Wyoming.
But there is a ton of praise from SN compared to the base map. Is SN perfect, no. But its fun. Very fun. Despite the bugs, its much better than the map map and I think after hearing about it so much, SCS committed an actual team to it. Based on the Vortex interview that Pavel did this past Summer, I'd like to think that Pavel is taking things in the right direction. Several things he said in that interview intrigued me. It was in Czech but there are English subtitles. I had to pause a lot to make sure I understood everything, but very very informative for me. I think the future is a bit more positive.