I was goung to put this in a comment on the post B214 created, but felt this deserved its own blog post.
I thought about how angels and fallen angels have different number of wings depending on how powerful they are. So I thought why not the devils? They vould incorporate the number of wings into a devil's status and strength. The only devils we have seen with multiple wings are Vali and Rizevim. So just my idea:
2 wings: Low-class devil(Entry-level for reincarnated devils. Also for pureblood low-class devils and half-blood devils who join a peerage.)
4 wings: Mid-class devils(Devils being promoted to mid-class devil get an extra pair of wings befitting their status. Also is given to pureblood mid-class devils who join a peerage.)
6 wings: High-class devil(Devils who were born into the 72 Pillars and Extra Demons. Upon registering as a king when coming of age or joining another high-class devil's peerage will grant them 3 pairs of wings. Before then they just had the two devil wings they were born with. Also mid-class devils getting promoted to high-class whether they want to be a king or not get an extra pair of wings.)
8 wings: Ultimate-class devils(High-class devils upon receiving a promotion to Ultimate-class will get an extra pair of wings.)
10 wings: Satan-class devils(Upon gaining strength equal to a Satan,Maou, devil king, or whatever you want to call it, Ultimate-class devils will receive an extra pair of wings. This is the first and only rank that is given ENTIRELY on the strength of a devil itself. They are still Ultimate-class devils. They just have the strength of a Satan without being one themselves.)
12 wings: Satans and Super Devils(For those devils who have become a Satan or become a transcendental being or both. The highest level a devil can achieve.)
There are some devils this system won't work on. The Phenex family because they don't have traditional devil wings and the same with Issei's children. And also those devils that are not part of a peerage or have their own. And assuming that the child of two reincarnated devils take the status of their parents, they can be included in high-class devils. And assuming that Issei's half-blood children(the children he has with the non-devil girls) will be high-class, we can include them in the high-class category.
Just would be interesting to see that in the future of the Underworld. Tell me your thoughts about it.