Yes, there are a lot of operations that can be implemented just in terms of bind and return. It is possible to make some functions more efficient by implementing them directly but having a generic library to fall back to would help with consistency. For instance both `lwt` and `async` are monadic, but `async` provides a richer API. I think having a generic monad library would help to bridge the gap a little bit*

* Since I am only dabbling in OCaml and only use `lwt` and `async` occasionally I'm not entirely sure. But judging by the usual structure of Haskell libraries, it should help

Yes. You can implement sequence/traverse/etc. for each specific monad in OCaml, but if you want to write a generic implementation that will work for any monad then you need typeclass-like functionality.

Not necessarily. You can manually pass in the module for the monad using first-class modules and then define the functions in terms of that. You could also define those operations in terms of monads using a functor if you want it to look more like Haskell.