Not really, when I was doing my prototype of moving everything into the SplashScreen class I had set the onload to be true. However, the problem is one of timing. First your activity that extends DroidGap gets loaded which then creates a CordovaWebView which in turn loads the PluginManager. The PM is responsible for reading plugins.xml and loading the ones that have onload set to true right away.
All of that is enough of a delay for the user to notice that the SplashScreen is not display as soon as the Activity is created. Also, the DroidGap class was sending a message to the plugin to show the SplashScreen before the class was instantiated so the message was lost. So, it looks like we'd need to queue up that message until someone is able to act upon it which is a non-trivial change.
Plus, does it even make sense to move all this out to a Plugin considering that someone who'd be embedding a CordovaWebView in their own app probably has their own plans for a SplashScreen.
Anyway, I will circle back to this once the great Camera cleanup is done.