I would ask the usual questions:

1. Are there examples of code bases using Fenwick trees?
2. What value does std::fenwick_tree provide over vcpkg/conan install?
3. What coordination problem does having it in the standard solve?
4. Is there evidence that users are suffering from not having a std solution?
5. What is the size of the cohort that will benefit from the std implementation
6. What is the quantitative cost of standardization plus ongoing maintenance, versus the measured benefit?

Thanks