Personally, putting a Supercharger in Emporia, KS would make some of the travel along I-35 easier. This was planned (permits were filed) a long time ago, but was nixed as the host site (restaurant) went through ownership changes (national franchise to independent) and then closed.
Having the Olathe, KS site completed would further make travel along I-35 more convenient. Currently, you're diverting around Kansas City while traveling along I-35.
I don't travel this stretch often, but the gap along I-40 from Oklahoma City, OK to Little Rock, AR is on the long side. There are 3 tentative sites on the Find Us page. Any of these would greatly help for travelers along I-40.
After these and completing out I-94 in North Dakota, I think you start getting into moving off the Interstates and onto US highways to enable more direct travel by avoiding roundabout travel as well as to open up areas of the country that are just not near an Interstate.
Having a stop between Springfield, MO and Miner, MO would allow easy travel along that route for people that don't want to drive 100 miles out of their way to I-70 or I-40 for East/West travel through Missouri. Currently, you need almost a 100% charge to make the 241 mile jump between these sites, especially in cool weather.
Stops along US-54 in and US-400 in KS, CO, OK, TX would open up those alternate routes. Traveling from Wichita, KS to Tucumcari, NM is 6h59m along US-54 and 7h37m along I-35/I-40 according to Google Maps. One or two stops along that route would open up the whole area to travel.
Travel along US-54 lets you see the largest hand dug well. You don't see those when traveling
along the Interstate.
Maybe the way to accomplish this is to look at locations that make jumping between I-80, I-70, I-40 possible without having to travel East/West to somewhere there is an existing Interstate. Double up those functions of putting extra locations on East/West US highways that are located along N/S highways that jump between these major interstates. A location like Liberal, KS would be nice for that since it's at the intersection of US-54 and US-83. That would make travel between the existing Colby, KS and Shamrock, TX Superchargers since it splits the leg into 173 and 146 mile legs. This also splits Wichita, KS to Tucumcari, NM into 212 and 209 mile legs. With the lower average speed on US highways, this would be doable with the larger batteries, but would require some care.
Frankly, Tesla should be looking at all the navigation requests entered into the in-car navigation system and flagging any route where their Trip Planner redirects the trip more than X miles to find a Supercharger along the route. This will have a little bit of garbage data because some people pre-plan on a web site and then just manually enter the supercharger stops into the nav as they go, but it should be good start for answering this question. Tesla has the big data and should be using it instead of asking for our self-centered answers (the person from Wisconsin says sites are needed in Wisconsin, and I say sites are needed in Kansas and the areas close to me).
