Battlecruiser utility depends on relative speed

Could rebuilt battlecruisers retain a useful role as battle-line speeds increased?

Only with a clear speed margin, potentially around 35 knots, because successive treaty battleships would become faster.

A viewer suggests that battlecruisers retain a place while battle-line speeds stay below about 27 or 28 knots. Their role depends on creating a much larger speed margin, potentially through reconstruction to 35 knots or more. Early treaty battleships might make 28 or 29 knots, while later batches could become faster as the design evolves. Battlecruiser utility therefore depends on contemporary fleet speed rather than a permanent quality of the type.