
My idea would be, depending on the "kind" of tab (Browser, Image, Compare, Slideshow, etc., etc.) that the user could select what appeared on the preview panel. Some ideas would be:
Image (or compare) preview
Tool bar with user definable buttons such as previous/next, rename, category, rating, close, etc.
Various image stats (path, resolution, EXIF, IPTC, etc.)
Histogram
Folder stats (for browser tab)
Having this stuff in a mouse hover panel below (or above) the tab saves screen real-estate, is local to the image, and IMO could potentially simplify the interface. A user could turn off all toolbars, status bar, (even the menu?) for an ultra clean interface, but still have access to tools that appear when mousing over the tab.