I disagree with you that the choice would be confusing. In truth, it would be LESS confusing than what we have now. Reconsider the fact that the vast majority of passengers on the Cardinal are coach passengers. Under present circumstances, a prospective passenger wanting to go from DC to White Sulfur Springs on Thursday is told that there is no train between these two cities on that particular day. THAT is confusing. However, if Amtrak runs a supplemental all coach train, he or she can make a reservation, buy a ticket, and be gone any day of the week. The average Amtrak customer does not care that the train to White Sulfur Springs on Thursday is a different name and different number than the one that runs on Friday. All he or she cares about is that the train is running and that seats are available.
Think about present circumstances between Indianapolis and Chicago. Talk about confusing - THAT ONE REALLY IS! Passengers who travel from Chicago to Lafayette on Sunday ride in a flimsy Horizon car with no leg rests and may or may not have food service. If he or she travels on Tuesday, they ride in an Amfleet II and have access to a diner/lounge car. If Amtrak ran a supplement to the Cardinal, these passengers would have the same service every day of the week.