EVD defines an eventType as:

<wsevd:eventType name="xs:NCName" element="xs:QName" actionURI="xs:anyURI"? ...>
    xs:any*
</wsevd:eventType>

Notice that the "element" attribute is required.  Normally this makes sense
since we would expect at least some data to appear in the soap body.
However, it seems like it might be possible to have situations where the
only thing that's needed is the actionURI on the notification msg.
For example, wsman defines hearbeat messages that an event source might send
periodically so that the sink knows the subscription is still alive.
In these cases the soap Body isn't needed at all so does it make sense
to require someone to define a GED in these cases?

Proposal:
Make "element" optional.  Add "OPTIONAL" to the defn of @element:

/wsevd:EventDescriptions/wsevd:eventType/@element

    This _OPTIONAL_ attribute refers to a GED defined or imported in the /wsevd:EventDescriptions/wsevd:types element. The referenced GED serves as the definition of this Event Type. 

and modify the xsd to match.

Also, in eventing we would need to tweak the EVD binding sections.

for example (see *** text):
The [Body] property of the notification has a single child element. This child element is an instance of the Global Element Declaration referenced by the element attribute of the wse:eventType element corresponding to the type of the event being transmitted.  *** If the element attribute is absent then the [Body] property has no children. ***

and

The /soap:Envelope/soap:Body/wse:Notify element has a single child element. This child element is an instance of the Global Element Declaration referenced by the element attribute of the eventType element corresponding to the type of the event being transmitted.  *** If the element attribute is absent then the wse:Notify element has no children. ***