This is a long time in coming.
The Hoosier Heritage Port Authority (formed by the cities of Fishers and Noblesville, and Hamilton County) was formed to buy the Nickel Plate line from its southern terminus (10th St.) to Tipton for possible use as a commuter heavy or light rail corridor. The Indiana Transportation Museum in Noblesville used much of the track for tourist rail operations, including a commuter-like operation to the Indiana State Fair. Within the last two years, a furor arose concerning the Museum's track maintenance and crew training, and the Port Authority locked ITM out from access to the track. Subsequently, the cities of Fishers and Noblesville have proposed tearing out the track between the two cities and converting it to a biking/walking trail, without any further discussion of using the ROW for commuter rail.
The Nickel Plate right-of-way was not ideally suited to commuter rail because it was a single-track line. Additional property would have had to be purchased (most likely by condemnation) for a second track, or else there would have had to be huge storage yards at each end and twice as much equipment purchased as would be needed if empty equipment could deadhead back on a second track for use again in the same daily commuter rush. Running time between the Fairgrounds and Fishers was 24 minutes, with a maximum authorized speed of 30, a few speed restrictions for track condition, crossing signal timing, and roadway traffic.
Another issue is that work locations are spread out in Indianapolis; while there are many who would go downtown, the north/northeast side just outside the I-465 belt has many large employers, and there are also many employers on the west side, north of the airport. There does not seem to be the same concentration of employers in downtown Indianapolis as there are in Chicago and some other major U.S. cities to make a commuter line with a downtown-only destination all that desirable.