"Wayland is a protocol for a new display server", "The wayland protocol is an asynchronous object oriented protocol", "The interfaces, requests and events are defined in protocol/wayland.xml". I don't see anything about "IPC" or applications that "can use this IPC to exchange any type of data".
> That Wayland is both the name of a protocol AND its default implementation (i.e. Wayland)? Or that Wayland protocol can be used to carry app- and shell-specific data?
The link you posted states that Wayland is a protocol and Weston is implementation. Have you read it yourself? ;-)