[spoiler discussion] General prediction on Arc 10
This is merely my thoughts on how Arc 10 might go:
During this Arc Subaru will get his Authority of Gluttony power and use it against Capella. (I'm starting to believe that Roy is genuinely dead.) Subaru's Power will come in the form of consuming a person's emotions making it easier to talk to them. (This Theory that I learned from Youtuber Conejotako EN) In Arc 6, When Meili returned to the LOTD a second time, Subaru kissed her hair while saying "I will sure to remember your worries and anguish" and she felt a sharp pain.
This is merely speculation but this type of authority would fit Subaru well. He could use this authority to get people to lose their fear of Capella and speak to him about what's really going on.
Another reason why i believe that Subaru will get his Gluttony power is because we don't have many arcs left in the story with 10, 11, and 12 being the final, so the plot line of the Sage Candidate needs to start progressing.
These just my thoughts and I can be completely wrong, but what do you think?