I have added a wish list item for this in our project tracker, but whatever we do sort on would be things that are already in the search index, it will not be related to other sorts such as the sort of a module on a page. 

There is not much in the search index that would be meaningful to sort on. Just as you can't sort google search, results should primarily sort by how well they match the search criteria. If you get too many results you should refine your search. If you click the help link next to the search button on the SearchResults page you will see information about advanced search syntax to refine a search.

Adding more stuff to the search index is problematic for upgrades because it would require all users who upgrade to rebuild the search index to get the additional data in there and for large sites this can be dodgy. So doing that would only be justified if it really adds significant functional value that a lot of people would want. 

Best,

Joe