Would it make more sense to change this:

    <!-- try to mount any mountable volume at all -->
    <ivm:Match name="ivm.mountable" value="true">
        <ivm:Option name="mount" value="true" />
    </ivm:Match>

to this: ?

    <!-- try to mount any mountable volume at all -->
    <ivm:Match name="ivm.mountable" value="true">
        <ivm:Match name="hal.info.category" value="volume">
            <ivm:Option name="mount" value="true" />
        </ivm:Match>
    </ivm:Match>