Of course, server-side implementations may be preferable in some cases to ensure that the information collected complies with your privacy policy.
Exemption is already managed by the Piano Analytics SDK; if the client-side cookie has the value 'exempt', the SDK will automatically modify the data sent to the selected endpoint. In this case, the synchronisation aspects do not matter as it is fully conditioned on the privacy cookie stored on the client side.
For the extended opt-out option, the SDK does not modify the information sent by the SDK. The information is cleaned when it reaches our processing, given the value of the 'visitor_privacy_mode' property. In this case, using a server-side implementation may also allow you to modify the payload of the event itself if you have specific privacy policies you wish to follow. This also applies to the exemption.