While it's very encouraging that the (current) technology is being developed by such a capable group, there are plenty of tangential worries to be had, especially if this is viewed as a "foot in the door." Who's to say such an emphasis will be placed on privacy going forward? Ultimately, this is the government and large corporations conditioning people to being tracked on an ongoing basis and blindly self-isolating themselves because they got a notification on their phone. It may be opt-in and privacy-preserving now, but my experience with governments suggests that's unlikely to remain the case for long.