Vova, We still have the logic that allows us to use reflection to get values in indexing, so basically the change is an additional check during the query processor start.
My concern regarding (2) is that a server node must have model classes in the classpath in order to check that we should deserialize values for indexing. If a server node does not have classes in the classpath and user still uses Externalizable classes on client, we will still end up with the same situation and it looks like we will not be able to detect it. Is there a way to tell that an object was externalizable without the class on server node?