The new train will add Milwaukee Mitchel Airport and Sturdivant both of which are very brief stops.
Car/driving culture in the United States is strong, but it is not impenetrable. I think policymakers and people who like to discuss these things (like us!) generally underestimate just how much people are willing to take alternative modes if they are safe, comfortable, reliable, and relatively time-competitive with driving. This applies across all kinds of travel scales, from walking and biking to public transit to high-speed rail.
Is an 8-hour trip from Chicago to MSP ideal? No. If you really want to make a dent in mode share along that corridor, you would run true high-speed service with limited stops and hourly departures. But this service will do relatively well. It provides a corridor-style option where it currently doesn't really exist, and is freed of the wildly unpredictable long-distance departure/arrival times on the existing Empire Builder. That departure time is actually just about right for someone along the corridor taking a weekend trip down to Chicago—you get most of your last day in the city to be a tourist, your point of departure is right downtown (and, crucially, not O'Hare!), and you'll get home at a not-totally-unreasonable hour.