The steemit condenser script unfortunately does not leave the src='data:' urls intact, it prefixes them with the steemit images redirect and then the images show up as broken.
I definitely see a use case where simple (well compressed) graphics would be useful to include inline, like for, basic subject oriented icons, bullets, or other simple graphical style-ups for a post.
I see where a user has posted an issue on github in regards to this, maybe enough up-votes on the issue will have positive results?
I also a little surprised that the user posts aren't in a secure iframe? Wouldn't that let them be more permissive as to allowed tags? I notice that even <span> tags are problematic, as well as the lack of inline styles of any kind (it seems a subset could be put into a whitelist of some sort).