It will be great if it have two column view mode, like StackEdit. Every time I'm writing a long post, it is frustrating to scroll down and up.
Sometimes I just write the post using StackEdit and then paste it here, but why doesn't Stack Exchange do it on its own?
Maybe most of time people are writing short answers, which do not need a left-right panel. However, in many cases, especially in math and physics sites, people are writing formula and derive. It is best to have a left and right panel. You can visit the math and physics site to see that many answers actually is very long and using and scrolling up and down is very unpleasant.
I can see that the editor area of the up-down is not fully used, the left side have some empty space and the right side is some link of hot post or something which is not very useful for editing. So I think if we can organize left-right panel economically, we will still have the same editing and previewing area as now we have.
I've measure the width on my computer, the middle area is about 15cm, the left area is about 4cm, and the right area showing how to format is about 12cm.