I have a theory
If Blackbeard challenges Luffy to a Davy back fight(an actual 1 on 1) but not what foxy introduced. We currently don't know if bb or someone in his crew can read poneglyhs. So it is safe to assume that only Robin can read it He may try to get Robin from strawhat through a Davy back fight.
We know Luffy is luffy, so he will accept the challange but this time he lose.
This would be round 1(Luffy vs blackbeard) after wano or elbaf.
If Blackbeard challenges Luffy to a Davy back fight(an actual 1 on 1) but not what foxy introduced. We currently don't know if bb or someone in his crew can read poneglyhs. So it is safe to assume that only Robin can read it He may try to get Robin from strawhat through a Davy back fight.
We know Luffy is luffy, so he will accept the challange but this time he lose.
This would be round 1(Luffy vs blackbeard) after wano or elbaf.