Wonderful post @timcliff ! A few others I think would be nice are

• Allowing to set the cover photo to not be the first picture in the blog post.
• See how the photo cover blog photo will be displayed and allow dragging and cropping to fit the window (approximately 1.73 x 1 ratio is what I use, but not everyone is savvy with photo editing).
• Possibly some kind of project curie for comments. Comments have become less rewarded as of late, likely in part that between a blog post and a comment, a blog post will almost always make more curation rewards.
• Ability to double upvote or triple upvote content you really like and wish to make more visible
• Possible separate voting power percentages for both comments and blog posts so that people do not have to choose between which they value more and give a comment voting percentage as well that allows for more upvoting of comments.
• 140 characters to say why you resteemed a blog post next to where you where the resteemed by text appears.
• @username mentions in other posts should have the user choose the ability to have it appear as an alert if they wish.
• Optional feed with video advertisements that major companies can pay to list (movie previews, new iphone, car etc.) and allow users to enter capchas to make sure the videos were watched. The companies can set how big the reward is to watch their video or offer discounts or coupons for their services.
• I actually like that their are no profile pictures, so people can remain anonymous and not necessarily be judged by their picture, but the content they make. People that want to make their image visible can certainly do that in their posts, but I like avatars.
• Make a users firt #introduceyourself post be worth 2x the normal value of a post. Making a good amount in the first post will encourage users to remain with steemit and should pay for itself in the long run. Possibly even 1.5x
• When you click promote, the option to directly tip a percentage of the promote value to the user. So if you promote $50 you could have a slider to give 10% to the user who created the post. So $5 would be sent directly to the user and $45 burned to promote the content higher.
I have many more ideas, but I think this will suffice for the moment :)