In what would almost be my hometown train, I want to share a local, non-expert perspective on this train, and were it stands. My core observation is it has the cards stacked against it.
First, to hopefully building on DDS&A's post, I will go with routing options and the challenges:
CN all the way, it seems Amtrak has a poor relationship, I’d have to believe without track upgrades, it might be dealing with a 60-mph route, think Cardinal, Hoosier State, the CN traffic seems like it could accommodate the train, but the route has lost two active siding over the years near Bartlett east end of Rockford, sitting in siding 30+ waiting for ..., again going back to the relationship .
Metra Milwaukee West / CP RR to CN Genoa, seems doable with a connection that would have to be build in a town, which leads to NIMBY complications. but three railroad, three dispatchers in 90 miles.
Metra Milwaukee West to UP in Elgin, Big Timber area, connector can be built, I believe they almost broke ground. To my knowledge the UP is “dark”, no signals, maybe a PTC waiver route with typically one UP train each way to Belvidere (auto plant) daily, but if PTC is a must, again cost and I’m sure, rightfully, UP would not want to pay for it or even part of it. Would this be another 60 mph situation? Then there are the tracks between Belvidere and Rockford, essentially a low speed branch that would have to be rebuilt.
Another possible option not actively on the table is a Metra Milwaukee West / CP to Davis Junction then up about an 11 mile CP branch to Rockford. One catch to this route would be no possible East end station in Rockford. Also the last segment would need work to meet standards. It is really one of the least complicated routing options.
Then there is the elephant in the room, I 90 Addams Tollway and the well-established bus service that starts with “Van”. I think the golden opportunity to start the service would have been when the multi-year rebuild was underway between Rockford and O’Hare, it was a mess. Now it is a true modern smart Interstate, 4 lanes O’Hare to Elgin, 3 lanes Elgin to Rockford. Smart lanes east of Elgin, and posted 70 mph from about 5 miles west of I 294 / O’Hare to Rockford, lighted all the way to add. I think most people are more than willing to pay the tolls for what you get. Then add a frequent, well-established bus service to boot.
The golden opportunity still maybe there for this route but it is not Rockford-Chicago segment, it is service to Galena, Dubuque, or even Waterloo, I know that is a long shot. US 20 is a mess west of Freeport to almost Dubuque, 2 lanes, curvy and busy, especially in the summer. There are plans to expand and reroute US 20 around Galena out there but last I knew, not in short term construction plans. Galena especially and Dubuque to some degree have tourism to help. To me it seems like Iowa or broke.