Your suggestions of platforms such as "SteemBay' are excellent. Not only would it bring added value, but it would surely attract new Steemers. Probably hundreds of thousands of new Steemers.
The other day, I had posted a link to Fishpond online bookstore (https://steemit.com/writing/@majes.tytyty/fishpond-online-bookstore-free-worldwide-shipping-of-books-cds-dvds-toys-and-more)
Subsequently, I became involved in some conversations about starting up a book exchange on Steemit. If we have a SteemBay platform, all Steemers can exchange / buy / sell anything, without having to deal with fiat currency or PayPal (PayFail, as I call it) or any such outdated payment systems.