FIFinderSyncProtocol.MakeListenerEndpoint is one of the new bindings in Xcode 9, on https://github.com/xamarin/xamarin-macios/pull/2219/commits/5d418bca55d1222ae3c8dac776d7413a1151e433. It relies on new Foundation bindings from https://github.com/xamarin/xamarin-macios/pull/2235#pullrequestreview-46117961, so once that PR is merged FIFinderSync needs to be updated to activate the binding
The NSXpcConnection bindings were actually moved out of the Foundation PR into a separate PR of their own due to the need for a sample to confirm they all work correctly before merging. The same PR also activates the above FIFinderSyncProtocol binding.
The xpc bindings is blocking this enough that it isn't happening for xcode9 timeframe.