Hi,
Before working on Object manager I decided to give a quick look at "Export bitmap" palette.
Here are tho mockups:
http://techwriter.nm.ru/mockups/mockup06.png (vertical orientation) http://techwriter.nm.ru/mockups/mockup07.png (horizontal orientation)
A few notes
1. I can easily imagine plenty of people who would prefer a longer input box for filename. No probs :) Just exchange "Output file:..." label and input box. That's it.
2. I've removed units switcher, because it seems to make no sense as we already have one units switcher in document properties which works everywhere. However it is present on one of first mockups (http://techwriter.nm.ru/mockups/mockup03.png).
3. I've placed a output file size counter label on the form, because it would be a nifty feature for those who does web design in Inkscape --- they always want to know how large the file is :) Besides otherwise there will be either empty space or a too large "Export" button.
4. I might be missing some feature plans for this palette. No probs, again :) I can redesign current mockups to make them fit your plans.
Alexandre