When I write a post in SO, I use to watch the markdown preview very often. It is a bless that it is updated in real time.
However, when my post is long, I have to scroll down the page to look at at the markdown preview, then scroll up to fix things in the edit. This happens especially to long posts because when I correct something at the end, the preview portion that interrests me is out of sight.
So I would like to suggest a Synced vertical scrollbar in the markdown preview.
The idea is to decide which portion of my post I want to see in it. Additionally, having both markview edit and preview panes synced when I edit my post should help a lot.