While putting together a view for #549 it became clear to me that users could use an exposed filter that would allow them to filter by author so that they can view all comments posted by a specific user. The best we offer in order to achieve this currently is by allowing to expose the Comment: Author as a text filter with a "contains" operator. Not very useful.
For Drupal, there is the Views Autocomplete Filters contrib module that allows exposing filters as autocomplete fields:
It would be awesome to have this feature available in core and we could use it in various admin views like the manage content and manage comments that have the author fields.