I feel Merlin's will be last told of the Sins imo after Escanor. Mainly because I think she will have a major connection to both the goddess and demon clans. I can see Nakaba slowly revealing Merlin InnateAbility/Sin/Past and race. Do you think he's left Merlin out of the tournament for a reason? I really wanna see her interact with Doler since she created Balor eye with his natural one.
I think she isn't there because firstly she would not be useful/could not be written into the tournament because she is just an orb, he is purposefully avoiding an Escalin reunion imo and i think she has gone to where Escanor's power level was at a few days back/gone to get Galan's body to study it or help reverse her curse? I think she is gone to do that or she is conserving her magic in the Boar's Hat!
Although Merlin's backstory may pertain to the goddess clan, i still can't see her backstory being before Escanor's who was literally just introduced close to 15 chapters ago. I feel like we will get Gowther's in this arc (before the 200's) and Merlin and Escanor's will be in the last part.
Who knows... maybe Escanor's sin also has to do with the goddess clan, but, it's on a whole other scale compared to the other sins?
Instead of committing murder, adultery, theft, arson etc... he did something that nobody in history could compare to?
That would be my guess on Escanor's sin, because otherwise why would it be Pride? He either needs to be proud of his sin, or he committed what i'm going to call the "ultimate act of selfishness"... or was going to!
I'm convinced Merlin's backstory is going to revolve around the goddess clan and when she falls she is going to be with Escanor for the last part of it!
Therefore, her backstory doesn't end as sadly as the others!