I wonder if Oceanic's possible diesel power plant would have been successful? The scale of the engines would have been far above anything else that put to sea at that time. (Actually, for about 50 years!)
I have read that the choice of power for Oceanic was never definitely decided, except for the fact that it would be electric. (Source: Power of the Great Liners) It is possible that White Star would have opted for a turbo-electric power system in the end. This would have lessened the development risk and had several advantages. (Full astern power available without the need to fit astern turbines, the ability to take a turbine off line and still keep all screws running, etc.)
If White Star had just managed to get Oceanic III to the launching stage then it is quite likely that she would have been finished and run with the Queen Mary. There would have been no need to build the Queen Elizabeth. An interesting what if........
Brent