Note: The afterword itself has no spoilers, save for the ending of the Aincrad arc.
The afterword of Volume 18 has been translated.
This is unusual for me, since I usually complete the afterword of a book when I finish the book first, but considering the recent news on what could possibly become SAO Volume 19 (Volume 18 spoiler warning!), we thought it would be a good idea to publish the afterword of Volume 18, since it contains some thoughts from the author pertaining to the future of the series. Please note that we have not begun work on this volume proper, and are still actively focusing on Volume 17.
As always, comments are appreciated.