WinmoJoe
Good news, I was wrong about this. :-)
This is actually possible to achieve. You can put something like this into the Subject line:
{autoarticle:1-| display:title| pict:0| order:publish_up,desc| onlynew:1|max:1}
or for K2 article (as an example)
{autok2:1-| display:title| pict:0| max:1| order:publish_up,desc| onlynew:1}
Please test your tag thoroughly before you actually send a campaign to your subscribers.