Since you plan to add a read status to comics, I believe this would be fairly easy to implement
I'm assuming you are going to have a table keeping track of the reading status of each comics for each user.
You could add in the same table, a column keeping track of comic's rating by user. This way we could have new benefits:
1: when opening the comics, provide ratings in the details window(and if the user has not put any rating, ubooquity could compute an average for all users)
2: folder (or any grouping), could display an average of the ratings for all comics within the folder/group below the image (again: display average for the connected user or the average over all users if no user ratings are available)
3: (in a future) a new sorting criteria for comics
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