Here’s a SVG with the basics…
Not too sure about the highlighting based on post interactions & markup. I think it might be quite good sometimes to have it automatically bolder if there’s a lot of interaction, but then it’s hard / impossible to differentiate from normal markup. (Also, it might be sometimes bad having that, another path to game the system…?)
Possibly markup shouldn’t allow bolding & different font sizes?
Or just no automatic weighing.