Random order thoughts:
The DE route has a lot more potential stops closer together than the current rail route from Indy to Chicago, and probably more than any route. In Maine you've got the whole string of beach towns, maybe not so huge in population but with lots of second homes and tourist destinations. In the tiny sliver of NH you've got a big university and you're in the commuting radius of Boston. And the route either belongs to a sympathetic transit authority or to a railroad without much freight business that is probably glad to have the DE.
Indy is a day-trip destination from within Indiana: big zoo and botanical garden approx 1.2 miles from the station; Indiana State Museum and Eiteljorg Museum of Western Art and Native American Culture (or something along those lines) under a mile from the station; minor league ballpark even closer to the station; football stadium and convention center close to the station in the other direction; Indiana State Historical Society museum under a mile north of the station; canal with paddelboat and canoe rentals in there; walkable-ish downtown with restaurants and whatnot basically between the station and most of those attractions. There's also a big children's museum that gets big travelling exhibits for adults, too, 3.4 miles north of the station and right on the Bus Rapid Transit Red Line with 10-minute headways and 25 minute trip time including the walking. Probably most of that would not bring a lot of people in from Chicago, except maybe the odd convention or football game, but I guarantee people from Lafayette and Crawfordsville make day trips to Indy every weekend and vacation day, and that on regular weekdays there are a certain number of people from those two cities going to downtown Indy for special work-related trips, or to do things at the state offices that are also under a mile from the station. I can guarantee the same thing for any direction you choose: Greencastle and Terre Haute; Bloomington; Muncie; etc. I can't guarantee that there are enough of those people to justify regional rail into Indy from any of those towns -- driving and parking are easy and cheap, partly because the city and state have based their development on cars and roads for 70 or 80 years and partly because the state leased a toll road for a gigantic lump sum and spend billions building and expanding highways in the last 15 years, with bare lip service to public transportation outside the NICTD area. (Some rural legislators are really nosy about blocking transit development in Indianapolis; I doubt light rail would actually have been better than BRT, but in any case there's a special law banning Indy from including any rail in its transit so they couldn't have even investigated it.) But there are a lot of day-trippers.
I don't know if there are a lot of Chicago-Indy business travelers, especially ones who live in a place where a day business trip by train from CUS would be more convenient than driving even if it were a fast train. But maybe there are. Lots of health ins and finance companies right downtown.
Indiana is very Indianapolis-centered. Most of the Interstates lead there. Part of the reason for building I-69 was to cut something like 20 minutes or half an hour off the trip from Evansville and Vincennes to Indy for specialized medical care. Indy suburbs are growing; Carmel is pretty much the Hoosier word for "fast-growing place of rich people" these days.
There is not good or frequent intra-Indiana bus service. I think TH has 2 a day to Indy, on Greyhound and one state-funded run via Bloomington.
Bottom line: Chicago-Indy travel is probably even harder of a sell than Indy-Chicago travel. The state has very little reason to want to subsidize Lafayette-Chicago travel. But Lafayette-Indy travel (or similar on other routes) might justify some kind of regional rail that was designed for getting people from the Hoosier hinterlands to Indy. Might, because driving is easy.
