I am willing to make a bold prediction. They will combine North and South Dakota and make it one big DLC. Probably called the Dakota's or something.
I think we can clearly see the pattern:
ETS: several full countries, part of the country (the upcoming DLC

) or the combination (the 2018-2019 DLCs) — the creative name for expansion pack.
ATS: one full state — just it’s name and nothing more.
So, we would probably see how the
ETS’s pattern will be applied to the
ATS — of course, if the developers will not go crazy and release every state as separate DLC, making the list as long as
ETS’s paintjob packs list

.