Permanent public file storage seems like a no-brainer to me.

If someone told me, you can post any file permanently and publicly as long as you have enough steem-power, I think steem would be front-page news world-wide.

The password thing is somewhat of a concern, but I'm sure someone could make a front-end password manager that would let people use the passwords they're used to.

And an integrated private chat/mail/message feature would definitely help facilitate commerce.

Thank you for sharing your insightful and original ideas!