Dh and I have been talking lately about adding another person(s) to our household. We like the idea of community living though where we live it is not possible for us right now.
There is a "poly families" thread in the Queer Parenting forum that is what you are looking for. I agree with you in theory on your idea, we tried it and it never worked out but then maybe we never found the right woman, and are now at a place in our lives where we're not looking for that. But I wish you lots of luck, I love the idea of extended family and lots of love.