I just realized something. I feel stupid for not thinking of it sooner. The Holding family owns the entire block the Little America and Grand America are on (at least I am assuming they still do). The Holding family has strong local ties. I was thinking the Sheraton lot would be a possibility for expansion in the future, but since the owners probably don't have strong local ties, I'm guessing they won't be terribly easy to work with.
Clearly, no part of the Grand America is going anywhere, but the Little America is different. It's comprised of both a main tower portion and the rest is motel-like. The motel portion occupies slightly more than 7 acres. I'm thinking the Holdings could work out a deal with Amazon. They'll continue to operate the Little America as is until the time comes when Amazon would need to expand beyond the 400 S Main block, and Amazon could then build on the motel portion of the Little America block. The main tower portion would stay. This Amazon development would be an incredible boon to both the America hotels, so I can't see the Holdings being against this.
Developing to the south of 400 S Main would also tie in well to the Patrinely development at 600 South Main.
Also, the portion of the county lot that hasn't been developed on yet is bigger than I thought. It's almost 1 acre. The main CCRI lot that would be offered is 10 acres. That brings the total acreage to 18 acres, or almost 800,000 sq ft, which is possibly enough room for the entire square footage needed.
That makes 3 owners, all who would have an extremely vested interest in bringing Amazon to the southern end of downtown.
Hopefully the city, county, LDS Church, and Holding family are already talking to each other about this but I have a fear that they are not.
Here's a map of the parcels. Sheraton lot is in red, but I'm not including that in my fantasy anymore since it's not ideal. CCRI and empty county lots in green, Little America motel portion in blue, and of course the parking lot directly south of Little America is where the Patrinely development would go:
As you can see, Amazon would own over 300 feet of frontage on both sides of Main Street where Courthouse Station is.