Originally Posted by Rowsdower!
Perhaps a post-credits scene in Batman/Superman?
It seems like a standalone thing, since Barry is narrating it.
I don't see Snyder and Goyer continuing the trend of post credit scenes. Which I hate anyway. But I would actually make an exception if this was a post-cred in Bats vs Supes. It seems like a good trailer tease.
It makes me think of the very first teaser for Batman Begins, showing the tone with the voiceover from Bruce.