Eu- is a classic antonym morph for dys-, yes, and though rendered as u- is less usual it's still the same morpheme that one find in euphoria or euphony.

Both are classically used to name fiction places, starting with Thomas More eponymous book.

That said, neither eu- nor dys- are related to chronology or imaginative consideration on themselves, only about how desirable or awful the prefixed root is assessed to be in the judged situation.