Just to be clear: once you have any version of OCaml running on your Linux box, you can use opam to manage your packages, including your compiler package. This is the preferred way to deal with OCaml packages. You can then install 4.06.1 with it, or the flambda variant of the compiler, or anything else you like.
If you want the default on Ubuntu to be a more recent OCaml, then I recommend talking to whomever manages the OCaml packages for Ubuntu, which is an Ubuntu rather than an OCaml thing as such.