Interesting idea !

That makes me wonder if there is still the problem that sailfish can't run with any other user than nemo ?
Being able to launch lipstick as another user would add to what you already implemented having a custom home directory, so isolating user preferences (history, favorites, games progress, social accounts...).

On the list of related idea, custom firewall rules to limit websites that can be visited to a safe white-list could interest some people, not sure how easy that can be done in sailfish.