Except for cmdliner whose distribution is based on a Makefile so that it only depends on ocaml, that’s an issue with topkg, not with individual packages. Opening one there increases the chances that I don’t forget.
I don’t think it should be too hard to add (it’s already done with for .mli files). There’s likely just a few subtelties with packed modules (manually with .cmi hiding, not -pack) and/or module aliases, but unless I’m mistaken this should be a matter of mimicking the install logic that is in place for .cmx files.
Btw. anyone knows if there is an invocation to retrigger package that build depend on topkg in an opam switch ?