Is it possible, and if: how, to filter (a flat view) to only show files with attribute "SVN Status = modified"?
Not that I know of.
When I want that I use TortoiseSVN's "Check for modifications" command which generates a good view (and lets you double-click to see the diffs etc.).
You could sort the flat-view (non-grouped) by the column to group the modified items together but I don't think there is a way to filter on columns which come from shell extensions like Tortoise.
I've become a DO evangelist, if not only because of this forum.
I learn so much. Thanks again for this extended answer. I didn't know that svn option.