Alright, chill bro~ ^^; Um...hmm...well, I've always seen Celly as more of a caretaker...more Dom than any other character, really. Luna, however, would be adorable in diapers! Going off specific artwork, Luna is also said to go into "filly mode" when alone with Celestia, meaning she basically shrinks to resemble a young filly when they're alone. Hmm...I wonder what they actually do when they're alone. I'd love to RP that!
Oh, here's that comic:
http://bakki.deviantart.com/art/MLP-...Gala-209997804