A successor to NR-1 needs a new research requirement

Will the United States build an NR-2 to replace NR-1, or have uncrewed vessels taken over the role?

Only if a new research requirement needs a crewed specialist submarine; otherwise one-off research tasks may remain with newer systems.

NR-1 was a research system built to investigate particular undersea questions and support US Navy experimentation. Such vessels are often one-offs rather than the first member of a continuous class. A successor would make sense only if the Navy identifies research that again requires a crewed submarine with comparable capabilities. Uncrewed vehicles may now cover some former tasks, but their existence does not by itself decide the issue. The research need, not a desire to replace an old hull on schedule, would drive an NR-2 program.