I don't think they are going to pay too much attention to the "Royalness" of the name, so no Elizabeths, Victorias etc. But could see them going with a classic, lovely name that wouldn't be shocking within the Royal family but is perhaps not usual within the Royal Family (nothing too out there like Chardonnay, Ferrari or random placenames etc like celebrities do these days
I predicted Eve (or something similar like Evelyn, Eva, Ava) earlier & sticking with that but also will add Grace, Amelia or one of the more trendy names around now like Florence or something like a flower name. I think Anne & Patricia (that's Autumn's mother's name isn't it?) could be middle names.