> Maybe there's tortious interference stuff here that gives these claims more teeth than a typical defamation suit (I've come to roll my eyes at tortious interference, too; unless you're alleging really specific fact patterns I've come to assume these interference claims are also a sort of C&D "punctuation").

This is the big one to me, actually. If Matt used the announcement feature in the WP.org codebase to place an announcement in WPEngine customers consoles telling them they should not support WPEngine, but instead his for-profit competitor, WP.com, it's pretty hard to argue that that is anything but tortious interference.