Integrate with third-party apps
So terribly lazy (I know), but I'm unlikely to use this amazing tool, unless I can embed in my app. Here me out, I don't think you need to provide any source code access, just a minified service (like google maps etc).
By allowing apps to embed your editor, IMHO would be a huge step-up and competitive advantage in terms of allowing people to proliferate your success and establish a market position.
By all means force them to be pro users, and provide ways for them to get their data out using your tool to say have a postback link when a deck is edited, and to create a new deck etc. Also provide ways for app-dev's to get you new sign-ups as it could be mutually beneficial to have users able to create presentations in many online softwares.
Of course you still get users regardless of their affiliation and happiness with the app that has integrated so you are not tied together