Yes, it would take an extra train set, but it would be one of the simplest to add trains in the system.
Saluki south, Illini north, but should rename for the sake of consistency south of Carbondale.
I agree, having looked at the routes and distances more, that extending a daytime corridor train to Memphis is a worthy idea and should not be that difficult to do, provided CN does not say no. The daytime schedule would complement the CONO Chicago-Memphis overnight schedule very nicely and could be done with no or little adjustments to the current Chicago-Carbondale schedules. Memphis had 65,769 passengers in FY11 which are decent numbers given the 6:27/6:50 AM and 10:00/10:40 PM arrival/departure times.
The Memphis to Chicago driving time is given as 8 to 9 hours. So, with some modest trip time reductions from Chicago to Carbondale with the Grand Crossing project in a few years, perhaps some IL state funding for track improvements, remove some trip time padding in the CONO schedule for LD trains, say the Memphis to Chicago corridor trip time is trimmed to under 10 hours. Close enough to compete with driving and bus service. Memphis is a big enough city to serve as a anchor city for a interstate corridor train. Could be very successful. Just have to get TN to provide some funding.
If they don't have one, Amtrak should have a business development effort that focuses on starting up or extending corridor services on the existing LD train routes. The corridor service would help improve the cost recovery of the LD train by sharing station and support costs along the corridor part of the route, boost LD train ridership base, and pay for station and track upgrades. The very successful NE Regional extension to Lynchburg is a good example of where the LD train route provides a much lower barrier to starting up a corridor service. Chicago to Twin Cities is another example of a likely future corridor service over an LD train route. The more corridor routes the LD trains have to operate on, the more stable the foundation is in ridership, track maintenance, and political support for the LD trains.