Not really, it has never been much of a 'thing' if I am honest...we see folks ask about it off and on and then typically they decide to just do away with the war itself.
When it gets down to it the reasons you would bundle everything into a war file vs setting up an executable type setup don't really line up that well. A war exists in large part to provide something that you can take around to commodity containers and deploy seamlessly (at least in theory). When you are looking at embedding why would you want to tangle with all the overhead, extra classes, bits and fobs of deployments and classloaders when you can streamline all of that away and end up with something clearly deterministic in code, easily embeddable into test cases, etc. You can just easily mount the servlets and apply all the same filters and normal webapp tools directly in code and do away with so much...
FWIW we wrote a war runner ages ago called jetty-runner which quite a few folks still use today for executing war files.
It follows more of the traditional war file usage only outside of the traditional distribution letting you fire up a war from the command line.
cheers,
Jesse