This should be live here in a soonish, just finishing review on the PR.
Those screenshots you have will be resolved @Alteras
This is tricky, I am not against this, but it would be a pretty big change.
We render markdown in a TEXTAREA now, to do that fancy highlighting we would need to swap it to use Ace (which we ship) or CodeMirror (which we do not) or a custom ProseMirror setup (which would be very complicated)
I personally like syntax highlighted markdown, but I think a side quest in this department would heavily distract us all from the progress being made with the rich editor.