But what if you prefer a differently formatted one-box with a larger image? I could see that happening at some point.
Also, I would be a bit nervous about a change in behaviour here … the popular Topic List Previews plugin uses these images to create large previews on the Topic List (just as Facebook (and Fakebook!) does). They would look pretty awful at significantly lower resolution. We’d at least need a way to recall the original, generously proportioned, open graph image url on a rebake.
(btw, as aside checkout my How To which is rather pertinent given the Forum you link: