Maybe you want to be using EMF's 2.4's new support for content
types? There isn't much documentation for it though, but what else
is new?
Here's an example in the plugin.xml for the xmi plugin that defines a
content type for Ecore itself:
<extension
point="org.eclipse.core.runtime.contentTypes">
<content-type
base-type="org.eclipse.core.runtime.xml"
file-extensions="ecore,xmi"
id="org.eclipse.emf.ecore"
name="%_UI_Ecore_content_type"
priority="normal">
<describer
class="org.eclipse.emf.ecore.xmi.impl.RootXMLContentHandlerImpl$Describer">
<parameter
name="namespace"
value="http://www.eclipse.org/emf/2002/Ecore">
</parameter>
<parameter
name="kind"
value="xmi">
</parameter>
</describer>
</content-type>
</extension>