I think it would be a smashing success. The American Civil War or the War Between the States (depending on what part of the USA you are in is one of the most studied periods of history. If you look at the Napoleonic campaigns they are as widely popular in the USA as Europe. Its just a fascinating period.
Many of the games on the Civil War have been made by gaming companies other than the US such as the French AGEOD`s Civil War.
I would implement the brilliant idea started in Rome2 with leaders only being able to move troops and this would be the kicker to make a grand campaign that would be one of the top sellers for The Creative Assembly if they can ever get past the political correctness of the controversial issues that seem to have spread to modern pundit talking points.
Brexit already the PC and make us a game where Bobby Lee and Sam Grant square off - it would top the selling list - do the marketing and this will bear out as I already have.