It is really peculiar, especially since many of the Italian cities are best represented by CSs, and best fit, historically, the ideal of what they're supposed to be.
It is possible that they have one in mind to become a fully fledged Civ, perhaps Tuscany, the Papal States (especially since religious units have been fleshed out), or another incarnation of Venice. However there's nothing stopping them from changing the name of a city-state later, as they will almost certainly do for Seoul and Amsterdam eventually.
They are very conspicuous by their absence, which does make me wonder if an Italian city state DLC is on the horizon. But if that is the case, you could still have one or two (i.e. Venice if Firaxis is planning a Tuscan Civ, Florence if they're planning a Venice civ, or either if they're planning a Papal State civ). I don't think stopping us from guessing is a motive of theirs - especially since
we're already guessing .