I would love to play a slave girl to a committed Lesbian couple. They can either both be Dommes or a Domme and a Switch.
Perhaps they have talked about bringing a full sub/slave into their relationship for a while. A friend of theirs has had a crush on both of them for a while, and one decides to make her a birthday present for the other.
I'd like to see plot and character development, as well as some of the emotional stuff of creating a permanent threesome. Perhaps there will be issues of jealousy and insecurity to be worked through.