The benefit is certainly small, and it probably would discourage using the API. I don't think that the migration path would be tricky. The new package would just reexport Text.Printf when built with base < 4.13, and it would define it when built with base >= 4.13. All that is required is a build-depends line. However, people really shouldn't be using this API in library code. Other modules in base provide more efficient and more type-safe ways handle most of the situations I've seen this used for.
I've never used System.Console.GetOpt (I'm typically use optparse-applicative for option parsing), but yes, I think that would also be a good candidate. Since there are multiple competing approach for argument parsing in the haskell ecosystem, my preference would be to avoid blessing any of them with inclusion in base.
I don't feel particularly strongly about either of these, but their position in base feels odd. They both feel like the result of applying a "batteries included" mindset to a standard library that has by and large refrained from including batteries.