I've never felt the need for a live preview for single pages, as the markdown mode syntax highlighting gives a very accurate representation of what the page will look like. I use cryogen for static websites, it has a local server that shows the pages generated from markdown.

I guess this is more of a vim question but I'd like to be able to interactively search and replace where the replace is dynamic based on the match. Is this possible out of the box in vim?

Say I want to turn all 1's into 7's and all 2's into 8's so on and so forth