Great suggestions! I added most of them to the list. A few were already there :)

select if you want a photo/image to be on its own line (text just above or below) or if text can be wrapped around a left or right centered image

They did add a way to do this recently, but it requires some 'expert' markdown skills. I'm not sure how it is done myself, but I have seen posts where people have used it. You could try searching through the existing markdown guides that are out there, and see if there are any good instructions.

not sure how feasible this is, but add a collection of copyright-free images that people can select from on Steemit (maybe users add any they use in posts to start this collection -- any found not to be truly free for use could be flagged/removed -- or search feature that somehow taps into an aggregate of free image sites)

If you haven't already, you should try pixabay.com in the meantime :)