I think I saw in one of the group. The person got this email when invited for test. After the oath was complete, (s)he got the certificate in email within 3 hours.
However the story goes further, when (s)he went to the passport office, the officers refused to accept this certificate and asked for original. They had no briefing about this. After a while a lady officer came in and mentioned to others that this is new pilot program and they will accept this certificate.
So be ready to face a bit of resistance at the govt office. If lucky, you may not.