We have always require that hard-wired are replaced with hard-wired, no exception. The wireless interconnected battery units are a great help to those properties that have never had hard-wired alarms and are required to provide interconnection between the alarms, but not as a replacement to an existing hard-wired system.
I try to get (non-enforceable recommendation) the owners to upgrade to a hard-wired unit with battery back-up (which is now required in all new construction) and if they’re updating anyway, make it a combination Smoke/CO alarm as that compliance date is fast approaching.
I do feel that the level is reduced, as I have seen far more batteries pulled out of alarms than hard-wired units being disabled. There’s nothing in them that the occupant can use for anything else, i.e. toys/remotes/etc.