Jacob has actually already appeared in the Brothers Apart series, and he will be showing up again! His premier came in Calling John Bonham, when he didn’t believe Bowman’s story of fighting against the lich with the Winchesters, so he called up the number on the business card to see if it was all true.

(Sam must adopt his lil bro Jacob, right?)

In Brothers Together, we don’t know what Jacob’s up to or where he’s at, so only the future will tell! It’s always possible to have any of our characters (especially our main characters) in any of the AUs.