In Governor Walker’s proposed budget bill, AB 40, there is a broad prohibition on local residency requirements which may invalidate any municipal residency requirement, whether it is enacted by ordinance, or agreed to under contract. If this passes, it is unlikely any municipality could enforce any residency requirements. It is possible that response time requirements (e.g. for police, file and other emergency employees) may be valid, depending on how they are written.
You can find the proposed residency preemption language in 66.0502, of AB 40.