As a user of Journey for a few years, I have come to appreciate the extensive features of their WYSIWYG editor, that Diarium lacks. This includes headings, tables, indented lists/bullets, blockquotes, and horizontal lines. They're excellent for making more fancy entires.
Personally, I make the greatest use of blockquotes (for obvious reasons), headings, and horizontal lines (breaking up sections with them is great), so that would be the ones I would want to see most.
Having discussed this already with Timo, it seems that these are incredibly difficult features for a solo developer to work on and very time-consuming, so it would be great if there was further interest beyond me and I could check back now and again to see if this is ever implemented, would make me switch over in a heartbeat.