With version 1.31 if the instance has been previously launched and then stopped, the plugin will automatically start the instance. I'm presuming you are talking about the initial launch here. Is that right?
I'd also like to see this happening. I've pre-configured the AMI which the EC2 plugin uses so that the Jenkins agent gets downloaded and installed on boot, kind of as described here: https://wiki.jenkins.io/display/JENKINS/Amazon+EC2+Plugin#AmazonEC2Plugin-ConfigureAMIforSpotSupport
However, Jenkins still insists on SSHing to the instance, even though it's not necessary. Yes, this is about the initial launch.