If Cuba hasen't issued a petition for an enabling act to Congress by the 1930's, that's a pretty clear sign they have no desire to ascend to Statehood. If there's a clear-cut desire on the part of Cubans to become a state, on the other hand, I don't see how politically Congress is going to be keep it delayed overly long; its just hard to find a justifable legal arguement to reject it. Puerto Rico has more than enough ambiguity in the desires of the population and the fact that its not financially self-sufficent to allow the question to continue; Cuba was far more populous, economically vibrant, infrastructural developed ect. and would be increasingly akward to ignore if they were vocally requesting the right to at least draft a Constitution.
... now, once that draft takes place they can, like the debate over the Mormons, drag out Statehood discussions based on specifics like this. Then we have to figure out just what terms Congress is going to insist on Cuba accepting in exchange for statehood (At the very least, a gurantee of education taking place in English is probably going to be insisted upon if nothing else). Having a broader assimilationist movement taking place with, for example, the AmerIndian boarding schools and influx of Eastern European immigrants to urban areas just when you have the rise of the mass public schooling, could easily combined with Progressive ideology to bring the "Using Schools to make Citizens" philosphy to its logical conclusion by placing earlier Federal requirements on states for language, civics education, ect. to make 2nd Generations at least Americans in thought and tounge.