Thinking out loud, this could be a good use case for the :first-child or :last-child pseudoselectors. This will let the browser determine how to display the empty list message based on whether there are any other streamed elements rendered.
I got an example working by adding the following line to the .table core component as the first <tr> before the streamed ones. You could also add it to the end and use the :first-child pseudoselector instead.
<tr class="hidden last:table-row"><td>No Streamed Items</td></tr>
https://github.com/codeanpeace/live_cal/commit/cbdda424d6d352af9c240734c334207016651d4b
