You’re talking about supporting ‘UE3’ packages - so I assume you mean packages from Unreal Engine 3, or UDK. They are not compatible with UE4, they will not work or import. UDK also uses Unreal Script as a programming language not C++, they are fundamentally different.
Also, the rules regarding UDK/UE3 content are not the same as UE4 content. Check the FAQ for info.