- Using / for italics is nice except it prevents you from writing stuff like "I love/hate it". (Or Unix paths, for that matter, but that could be addressed by point 3 below.) Would requiring a space before the slash but not after for an opening italics and a space after the slash but not before for closing italics be enough? I'm not sure. I dislike heuristics like these because exceptions always appear. My first guess at an exception: how would you write something like, "I said, 'Whatever.'"?
- Similarly, trying to automatch quotes is out. As I wrote in a comment: how would you parse "He said, 'Where are you goin'?'"
(The difficulty is in detecting that the apostrophe following "goin'" is not the closing single quote. You can't rely on punctuation preceding the close quote because you could just put a word in 'singlequotes'.)
- We need the equivalent of the TeX "verbatim" environment, in which your text is not interpreted at all. Unfortunately, this is a classic problem in meta because it then prevents you from using the closing verbatim marker within the verbatim text. To copy TeX's style would mean you write something like "#ohello thereo", where the # signals that the next character ("o", here) is the delimiter for the verbatim text, so you can choose it carefully so it doesn't interact with your text. But pound won't work there, will it?
- What should the blockquote character be? Structured text uses indentation but that's a bit difficult to type in this sort of editor. (I'm leaning towards tilde.)
- What should the monospaced character be? Or...
- How about LJ user tags? It'd be fun to link to a user by typing something like "%eru".
- How can you type normal HTML tags? Using the verbatim environment? Or should the verbatim environment escape HTML characters?
I'm tempted to just grab one character as the generic LogJam command character (tilde is a good candidate because you shouldn't be using it in normal text), except that starts moving away from simple typing. I think supporting a reasonable subset of HTML and allowing the rest with HTML tags is preferable.