Elementary roadmap

The following features are ordered according to their importance and ease of implementation

Short term

Review code highlight themes in preview
Fix syntax highlight in embedded html

Long term

Spell-checking
Subscript and superscript
Setting to show whitespace and non-visible characters
Translation
Outline sidebar
Custom themes / CSS
Open linked markdown files in Elementary

Distant future

Add new items to a list when return is pressed
Typewriter mode

Features to consider

Tags, wikilinks, etc.