You seem to bne open to different idea, great! ^^ Then Ill give you a bunch of raw ideas and let's see what would be most interestig for us both, should we?
Soul Eater. Can be Medusa getting diapered as a kind of punishment/reforming technique, or some of the Mester/Weapon pairs.
Rosario+Vampire. Either girls discover that Tsukune has a fetish for diapered girls and al start to wear diapers and demand being changed or are victims of some weird curse...
Flip Flappers. With the canon age-regression and mommy issues it's really easy to turn it into AB/DL story with hints or romace and saphic eroticism.
Revolutinary Girl Utena. First of all, I'd love to do anything centered around Tsuwabaki and/or Nanami, but i'm willinmg to discuss almost anything based on this fandom.
And if you saw this series of arts
https://diaperedanime.com/gallery/sho...hikuen/cat/509 - I'd like to try a kindergarden like this with characters from almost any fandom I know (see above and feel free to offer your favorites: I know most of the well-known animes like Naruto and Sailor Moon and many others).