Hey , sorry for the late response, things have been crazy over here for us and we've been nose to the grindstone so we can get this into people's hands asap.
We will give the user the option to use whichever password they are most comfortable with, whether that is their master password, or one of their other keys. The exact user flow for the final product is something we are still working on, but our intention is to create a user flow that recommends the user login with their posting key only.
RE: [Introducing Steemy] - Fully Native iOS/Android apps for STEEM