What got me to jump onto the WordPress band-wagon was the way its core worked … “the loop”. My JS isn’t nearly “up to par” when it comes to something like this, but primitives like sending email are accessed through “hooks” in a way I can handle. I create a plugin that hooks into the email routine calling other core routines to provide the specifics for that transaction i.e. post number, date, logged in username etc.

I’m interested to see you call it “extension”. In WP folk talk about “core”, “plugins”, and “widgets”.