The only way that it will make practical sense for a MBT that big at any point in the future: If they were to develop another form of power supply similar to your Nuclear power plant for Subs and Carriers. Definitely not nuclear for a tank, but that's the general idea. Essentially, you'd have to make the entire tank much bigger to make it practical anyways, so you're looking at absolutely pathetic range fuel hogging monster with an ordinary combustion engine. Some other power plant would be the only possible way to make the thing practical. Ultimately, I don't see a good reason to go with it, but its a fascinating idea.