Probably not, but a girl can hope, right?
Kristin dos Santos says that Mary McDonnell is guesting on Grey's for a multi-ep arc. You may know her as the president on Battlestar Galactica, but I will always know her as Eleanor Carter, John's crazy mom on ER.
No word yet on who she'll play, but KDS offers her own speculation: "Could this be the older woman of McSteamy's dreams? A hospital administrator come to help or harass the Chief? Or maybe Alex's mentally ill mother?"
I'd just like to throw out that I'd really prefer it if she played Derek's mom. If only because that would make Drs. Shepherd and Carter brothers by association.