I think markdown is pretty great for what it does, but I've been having concerns with regards to how accessible it is as the only way of writing posts. Far too often, I run into problems where I forget that a newline requires a double space and my posts come out completely different in the preview than they do in the editor.
For small posts, this isn't always a huge problem, but it can be very tedious/difficult to fix little markdown issues like that on a long post because you expected the post to look the way it does in the editor. It's also way too easy to forget stuff like this, make your post, and find out only after it's been posted that your post looks completely different from what it looks like in the editor.
What I propose is that there should be a WYSIWYG editor. Heck, it could even be a direct copy from the editor of this forum. Being able to switch between writing your posts in markdown or WYSIWYG would make things a lot more accessible and reduce headaches and annoying moments of "oops, forgot to add a double space at the end of a line"