Billie Piper apparently would like the role and may have a good shot at it. I think she'd do well. And there is a precedent for a Time Lord regenerating in the form of someone else -- back when Romana regenerated during the 4th Doctor era.
No hurry to boot Tennant though, I hope. He's settling in as well as Eccleston did ... and those weren't easy footsteps to follow in.
It's been a bear getting a complete episode off usenet and YouTube has been a spotty resource as well. Keeping an eye out now to Sci-Fi will pick up the second season. They're doing a woeful job promoting the show and the ratings don't look that hot, despite the fact it's the best thing they've got going.
