As far as I know, we have at least two “battle tested” implementations of vectors around: the one from Batteries and the one from Containers (I could not find one in base or core_kernel). There is also the code from Jean-Christophe Filliâtre: vector.mli vector.ml
I think it would be good to start by reviewing the interfaces of all these vector APIs and implementations, what they offer and how much they differ. Then we could discuss which code we want to import in the compiler.