Using <tt> allows to integrate with the existing code in a simple way. MOTD fixed font support uses another approach, but that would mean messing with the <font> tags, not sure if this is worth that?
Long term I hope I can rewrite the QTextDocument generation to not go via HTML, but directly add 'QText*' classes, and then update styling on text sizes changes (or on planned color theme change) via the 'QText*Format' classes. Might happen in the next weeks, or never ;)
Would %M be a good code for monospace? Other ideas?