camlp4 4.10 is now available in opam. Quoting the readme :
Later releases will try to keep camlp4 buildable, by supporting new OCaml AST but not new syntax constructions, which means camlp4 will be able to parse only OCaml language up to 4.08. Rationale: existing code using camlp4 will still be buildable, but no new code should be written with camlp4.