I wrote a Quit extension for Epiphany. Took me all of maybe 45 minutes.
I'm planning on updating the "Writing Epiphany Extensions" guide. There have been a few nice changes in the Epiphany source code which should be reflected in the guide: slots for attach/detach of tabs, XML extension descriptions, and toolbar buttons spring to mind.
Along the same line, I think I'll create a new script similar to my (little-known) copy-template script. It'll create a new standalone Epiphany extension -- just add code! (The copy-template script creates a new subdirectory in epiphany-extensions/extensions -- great for *us* but I imagine a large part of the guide's target demographic doesn't care).