Diesel re-engining the Reichsmarine's old battleships

Would earlier German large-diesel development lead to re-engining the predreadnoughts retained after the First World War?

Yes; efficient diesels would suit slow treaty-retained ships by improving range and economy even if they could not restore frontline speed.

Germany was already studying large marine diesels before the First World War, but the necessary power density matured too late for the oldest ships. Moving that development into the early 1920s makes a postwar re-engining program plausible. The retained predreadnoughts were not going to become fast ships, so fuel efficiency and operating range mattered more than a marginal speed gain. The scenario shows how treaty-constrained fleets can use machinery modernization to extract different value from obsolete hulls.