I think that IND could work, as the population base is higher than many think. Think about it this way: Indianapolis is the only large airport in Indiana, a state with a population of 6 million people. Though you have ORD and CVG near many of Indiana's residents, ORD is extremely congested and ops at CVG are going to be lessened by the Comair strike, as they supply more than half of the air traffic at CVG. And if, God forbid, Comair went under, CVG would not provide very many connections, as Delta itself does not operate many domestic flights out of CVG.
SAT would be a good pick, as San Antonio is a very large city, but the amount of business travelers are very low. Also, IAH, HOU, DFW, and DAL connect many travelers from SAT. A well financed startup (like jetBlue was) may be able to siphon off some passengers with a large initial service. This means nonstops to at least seven or eight large markets with fairly frequent service. But it would always have low yield unless the amount of business travelers increased.
When dealing with this type of topic, you have to look at secondary airports that serve crowded markets, such as large metro areas. A perfect example is Houston's Ellington Field. The demographics are there. Two long runways. (around 10,000 ft.) The runways do not intersect, which means you can have at least 60-80 operations an hour (factoring in surrounding air traffic). Ellington is the closest Houston airport to the large factories and industrial complexes that make up the IH-45 corridor from South Houston to Galveston. But once again the airline would have to be well financed, as price cutting from WN and CO would kill the airline off. Also, a terminal would have to be constructed, costing the airline millions. That would suck for a startup. Thanks for reading.