I don't think there's a trade that makes more sense.
Baltimore isn't going anywhere and Carolina is contending.
Panthers biggest weakness right now is lack of receivers. Smith is playing terrific football this season and Carolina could definitely use his explosiveness, play-making ability and experience.
There's no reason Baltimore wouldn't accept a 5/6th round pick in return.
It's tank season for them.
His ending in Carolina was not a good one. I highly doubt the team or him would have any interest in a reunion.
And if Baltimore moves him, who plays WR for them? There are still games that need to be played, can't have a bunch of practice squad players out there. If Flacco is out there taking coverage sacks it puts the team in jeopardy for more than just this year