Nuclear deterrence has been one of the most efficient means to prevent a new conventional world war. That is why large powers, starting with the U.S. and Russia, put so much resources into building the next generations of submarines. As a priority in most military budgets, including for some smaller powers like the U.K. or France, nuclear submarines concentrate all the latest technologies. That is why looking at the submarine of the future make sense for futurists. The new submarines might become underwater platforms - almost like underwater aircraft carrier - carrying a lot of new weapons and equipment such as drone and submarine drones. They might not become unmanned in the short or medium term, but the crew will probably decrease in size, with more comfort and possibilities to communicate for the sailors onboard. It might be the place to deploy new applications of quantum computing and to use the latest nuclear fusion engines.
To know more about all this, here is a very informed article by H I Sutton, at Forbes: https://www.forbes.com/sites/hisutton/2020/08/14/what-the-ultimate-submarine-could-look-like-in-20-years/