According to this thread here, there are no plans for the Air Jordan XX4 shoe. It makes sense to stop at XX3 since Michael Jordan’s number was 23 and he no longer even plays basketball either.
Apparently there will be an Air Jordan 2009 signature shoe that possibly will take on the next incarnation of the AJ lineup.
I got my first pair of Jordans when the original VIs were released. It’s been a long time coming and I never would’ve thought about the day when they’d end the actual numbered Jordan sneakers. I guess all good things do come to an end.