As noted in P. Weinberger's revisit of Louis de Broglie's 1924 doctoral thesis:
De Broglie's contribution in the Philosophical Magazine from 1924 is fascinating from many standpoints: for its moderate use of mathematics, the close connection to Einstein's special theory of relativity, and of course for the proposal of matter waves. We revisit this mostly speculative publication, which contributed crucially to the birth of quantum mechanics.
Although probably not publishable in today's environment, due to being purely speculative, the paper did win de Broglie the Nobel Prize in physics only 5 years later, for his ground breaking hypothesis of wave-particle duality, after experimental verification of his hypothesis was obtained.
The paper could be contrasted to the Michelson Morley experiment for the complementary way in which both experiment and theory are complementary essentials to the development of new physics. Sometimes an experiment thought to be routine provides a result totally unexpected; and sometimes a novel idea must be conceived so that one can look for the unexpected.