We have been developing a set of utilities (similar to what we did in DTM) that we are calling "Useful Things Adobe Should Have Cooked Into Launch" (granted, it needs a less unwieldy name!). We can load in in custom JS and make the functions available at the window level, but if we could cook it all into an Extension it would be easier to deploy across all of our properties.
Quick update. I wrote an extension that has an action that will create a window-level object that has the various utility functions. Seems to work OK (VERY limited testing) - I was able to execute commands from the console.
The only downside is you have to run the action in, say, a page load rule to make them available. Is there a place to put code in an extension that runs regardless of whether or not an action is called?