I considered this a little, but I want to optimize for a more robust set of features in the future that would require an account... E.g. eventually handling the submission to the marketplace for the user, etc. + I was worried about users potentially losing lots of work if LocalStorage gets wiped for some reason.
maybe make the changes they make in-memory-only and prompt them to sign up to persist. Like what piskelapp.com do - you can edit an image and save it locally, but if you want to save it to your gallery you need to create an account.