My first impression is somethere where the TransAm intersects another major bike route. The hamlet in Colorado south of Pueblo-Canon City where the Western Express meets the TA is one option, but it's only half a day's ride to Pueblo, so probably not much demand there.
Lolo or Missoula, MT are obvious choices, Lolo because TA riders hit it twice in between the pilgramage to Adventure Cycling headquarters, and Missoula because you have the intersection of the TA and Lewis and Clark. But again, Lolo's half a day from Missoula, and there's plenty of infrastructure in Missoula to support touring cyclists.
If you want to see a lot of bicyclists, go to Damascus, VA on a summer weekend and watch the people coasting down the Virginia Creeper trail. Of course, most of those people rent bikes in, and are shuttled up the mountain from, Damascus. Cool vibe in town because you get the intersection of the AT after a long dry stretch, bare of towns, and the cyclists add to the visitors. Do they need another hostel? Maybe, maybe not.
I've not been there, but I've heard the Minnesota rail-trails are generating some traffic, at least in the summer. Local merchants (including motel and restaurant owners, and B&B operators) are taking note, especially near where two intersect.
I think places like Twin Bridges, MT, or Hindman, KY (Knott County), work well because the people who live there decided to do something, and did it right. It's going to be harder to set something up and generate a buzz if you're not already attached there. Bike touring in the U.S. is seasonal, and still so unusual, that you might be better off picking a place you'd like to live on or near a major bike route, and set up something there.