Jumping the licensing shark

Right, adding additional permissions to copyleft licenses is fine, and as far as I know can never add incompatibilities (although it would be nice to have a lawyer confirm). In the case of OCaml LGPL + linking exception (which is this kind of "additional permission" license) it has never been raised as an issue in all the 20-ish years we've been using it. We just treat it like LGPL.