My understanding is that @dynamicMemberLookup is intended for cases where static declarations are not possible, or are completely impractical. In your bridging scenarios, Objective-C classes rarely have dynamic properties, in the sense that they are not declared in an interface somewhere.
You have also failed to explain why you would need a proxy object in the first place. Objective-C objects are directly accessible, after all, or the proxy wouldn't work, either. What functionality would such a proxy be providing, such that it would also be providing unbounded access to the wrapped object's properties?
In short, I don't understand your use case, and I agree with others that this seems counter to the intent of @dynamicMemberLookup.