Pieces considered a functioning road are vastly different from pieces without any gameplay function (ornaments) cause multiple factors are suddenly relevant - not just electricity but also fulfillment of needs, transportation of goods, buses, ... All these points would need to work and be tested for this case. And, as someone else pointed out: visually the stairs would not work with any kind of cart or car and cause all kinds of glitches and issues.
Additionally, the Cosmetic DLC specifically are designed to have no gameplay impact/function. We want to stick to this "rule" in order to make sure they're clearly separate from the regular DLC.