I wanted to turn private_in_public into deny-by-default before the next release and remove ObsoleteVisiblePrivateTypesVisitor after the next release, but still leave some noticeable rule changes (as opposed to just bugs) like pub type Pub = Priv; as lints for several more cycles.
There's also match_of_unit_variant_via_paren_dotdot which is quite old (more than half a year) and deny-by-default for months. It's totally ready for removing, I was just waiting for https://github.com/rust-lang/rfcs/pull/1506 to give it a replacement (I expected it to be accepted sooner).