I love Idaho. I wish some locals would have chimed in here for landmarks. I've spent five weeks worth of picture-taking trips here over the last few years, so I'll add a few suggestions.
My favorite area, namely along the Lost River Range between Mackay and Challis. The highway would need to terminate in Salmon until MT gets added, unless (see below) . . .
Arco would best be suited as a scenery town, but I would say this signature building could be added, maybe closer to the highway so it's visible:
I guess it could have delivery point to the grain elevator:
Sinage possibility for Mt. Borah, the state's highest peak:
Grand View Canyon is a short, but signature section along the highway. It's signed
on either end, but the signs aren't really visible on Google Maps.
I would hope ID 75 would be included in order to drive below the Sawtooth Range up to Stanley, then over to Challis. Hopefully, highway 21 as well through Bowman and down to Boise.
Having US 12 would be ideal up north to cut across the panhandle, but I don't know how much of Montana SCS would be apt to include initially. I guess they cut into Idaho for a little bit on the current release, and I think it would be hard to omit US 12, which is a great (and historical, relating to Lewis and Clark) drive along the river, and a main east-west route. That being the case, to me, it would make sense to connect Lolo with Salmon with the rest of US 93 at this time. I really hope highways 12, 21, and 75 will be included, as I fear Idaho is going to look too sparse on roads, as a few really great and super scenic roads didn't make the cut in SE Utah (12, 24, and 95), making that region empty.
So, if this little sliver of Montana is to be included, here is a large lumberyard with sawmill that could make for a drop-off:
Hamilton, and all the other connecting towns in the beautiful Bitterroot Valley could serve as a full-blown town with many industries in the map, but SCS may opt to simply use Missoula. SCS, you may wish to note the topography of the Bitterroot Mountains
west of the Hamilton area. They are very unique driving along, as you're able to look up a number of drainages, as opposed to being a solid north-south ridge of mountains. I'm guessing you'll be able to replicate that to a degree, but something I thought I'd note.
Edit: I just read the general discussion thread for the first time and saw ads678's rendition here
. He nailed it. That is the most ideal scenario. I might be inclined to suggest Stanley being a scenic town and Challis as a delivery town, as it's much larger, but either way, that layout is perfect.