This sign up thing is such a plague. I don't want to trade my digital identity for a theme, it's a bad deal. The only reason I would sign up is if you'd allow theme hosting and signing up would allow me to host my themes and gain notoriety.
That's fair. In the future I'd like to implement features like: automatically handle publishing to the marketplace for the user (right now it's a pain), upvotes system, etc. Accounts are a good solution for these types of features + it makes the theme data persistence way more robust so you can comfortably / reliably start a theme and then come back later to finish it. There are many suggestions for making signing-in optional though, so will explore this.