Yep, this is the big problem. There's simply no viable way to split into urban countries that hold and produce a vast majority of the wealth and the majority of the population, and have a massive swathe of the the most beautiful land in the US as a separate country or countries. It would make the most awkward-looking of maps. Although, on the other hand, splitting off into city-states is a pretty fun thought project. It'd impact the electoral playing field a bit more, as well as provide some interesting effects on congressional/senatorial representation. It'd also very likely deepen the rural-urban divide even further. But rural Californians might like being separate from its more populous city-state neighbors, and I know the city-state of Atlanta would just love to be free of its surrounding rural citizens. Cleveland would likely feel better about holding its own versus the rest of rural Ohio.

It's pretty interesting to contemplate what elections would look like if all states simply apportioned their electoral votes according to Maine/Nebraska rules, or a popular-proportion scheme, and disposed of the unit rules entirely.

Maine/Nebraska rules (1 EV to winner of each CD, + 2 to statewide winner) would increase the value (and thus incidence) of partisan gerrymandering, because then it buys you not only House seats but also Presidential EVs.

87% of Maryland lives in an urban area, versus 48% of West Virginia. Maryland would drift way to the left if it wasn't forced into political compromises to accommodate other states.

It's also more like 60-40 40-60, not 90-10 10-90.

That is, there are cultural differences between the city and rural majorities, but neither group is particularly homogeneous.