Now that there's family sharing, is it possible to migrate save files to someone else's profile? I know we can download them, but where would we upload them?
@Axtman No, I don't think it's possible to transfer a save from one account to another. Google Takeout is one-way; you can use it to get data out, but there's no mechanism for bringing data back in.
You might want to use the in-app feedback option to let the Stadia devs this is a capability you'd like to see added.