Depends on how granny she is. I don't really have any interest in seeing any of my favorite pornstars as beatup old women with saggy titties, blown-out assholes, and drooping pussy lips. Part of the reason I love the women I love is for their vitality and youth...
That being said, I am by no means anti-milf. Some women look better with age. Take Nin Hartley for example. I liked her when she was younger, but something about her now seems so much hotter to me. Same goes for Sharon Mitchell, Ginger Lynn, and Christy Canyon (god, I wish she still did porn).
I wouldn't mind seeing Jenna Haze when she hits milf-status.