When a destroyer becomes a cruiser

How long before a modern destroyer reaches Second World War battleship displacement?

The answer doubts it would happen soon under the destroyer label and expects a ship of that size to receive another designation.

A displacement of roughly 50,000 tons is suggested for the battleship-sized destroyer in the question. The answer doubts that such a ship would appear soon under the destroyer label, since much heavier combatants would need another designation. It treats the Defiant concept as a cruiser despite its battleship label. The discussion concerns classification and displacement, and does not establish a fixed tonnage boundary between ship types.