I see, that people think about ajax in the admin from time to time Django Admin Ajax List view and delete?. I think it would be great highly demanded built-in feature if you allow users to define on list view what fields will be dynamically fetched just on some action. For example on click of arrow or plus symbols.
I think that it will be needed to anybody who have a lot of data on this list view and this is one of key parts of functionality. The page download will be speeded up drastically. You will also get opportunity to compare this additional fields on the list view and don’t just open each detail view and compare the full pages.