Just saw this interview with Joss Whedon

Question: With Sarah Connor Chronicles canceled, please tell me there is a possibility of Summer Glau making an appearance on Dollhouse! --Jenn

Ausiello: The noise you're about to hear is the sound of the Whedonverse exploding. Joss confirms to me exclusively that, well, he's one step head of you. "If anybody thinks [bringing Summer onto Dollhouse] hasn't occurred to me already then they have not met me," he says. "I mentioned it to her before [SCC] was canceled. I was like, 'You know, we should get you in the 'house.' But first we have to come up with something that works." And casting her as a doll would not work, insists Whedon. "Summer would be perfect to play an active, but she's done that [type of role] a lot," he says. "I'd rather see her play someone who talks too much. The most fun I have is when I get somebody who's good and comfortable at doing something, and then I make them do something else. Summer said to me, 'I would like to play a normal girl before I die of extreme old age.'"

http://ausiellofiles.ew.com/2009/05/ask-ausiello--3.html

Oh man I would love to see this. I love Summer Glau and it would be great to see her guest starring. I hope Joss brings more of the old gang on the show