I would definitely be interested in such a library. Do you have a timeline for when you would release it? If the main blocker is simply choosing a license, assuming that the ultimate choice would probably be rather permissive I don’t see a huge harm in making the source available to view.
I am less familiar with the specifics of licensing in the OCaml ecosystem, but I have given it some thought generally. If you want a permissive license, I would support Apache 2.0 (alternatively, licensed at the licensee’s choice of Apache 2.0 OR MIT, if you care about GPLv2 compatibility). As I understand it, LGPLv2.1 + OCaml LGPL linking exception is popular in the OCaml ecosystem, but would be less attractive to me personally due to, among other reasons, the lack of an explicit patent grant (not that I anticipate your library to somehow be patent-encumbered, but it is nice to not need to think about it), the terms of section 2, and the comparative lack of discussion of contributions. The last point being less relevant if you also intend to have a CLA. But I am not a lawyer, and free advice is worth what you pay for it.