Lots of cool ideas here, kudos!
I also would love to see:
Steemit Video Uploads (pay to upload and or pay to watch, possibly)
Steem based music label
Steemit freelance market place. "Steemerr"?
The emergence of Steemit-exclusive celebrities, where Steemit is the first port of call for their content. (just like YouTube is the place to see Thunderf00t, for example, even though he has multiple web presences.)
A Steem based alternative to Tradebit, where people can buy and sell digital files. Huge scope for abuse though, unfortunately.