While I do not think it is a bad idea to add an optional way to write the contents of conflicted stages out to separate files, I do not think it is a good idea to change what happens to add/add conflict by default.
Two integrators picking up a same patch that adds a file separately and allowing them to diverge before they are merged should not be all that surprising, just like two integrators picking up a same patch that changes an existing path and letting them evolve independently, so from that point of view, I do not think there is fundamental difference between edit/edit vs add/add and rename/rename conflict. The latter certainly would be much rarer, but that is because edit happens a lot more often than add. There certainly are cases where conflicts is easier to resolve when the merged tip versions are unrelated or diverged too vastly, with or without a common merge base. As I already agreed to, it would be useful in such a case to have an option to write the conflicted stages to separate files to let an external merge tool to examine them and help you resolve them. But that is not limited to resolving vast differece between contents involved in an add/add conflict, is it? The same tool (which can be driven as a mergetool backend) would be useful in reconciling the difference between contents involved in an edit/edit conflict, no? If anything, if rename/rename behaves differently by always writing the result out to separate files, it is that codepath whose behaviour should be fixed to match how add/add conflicts are dealt with.