Honestly, I would think if you have not heard at all from Burr, than that boat sailed two weeks ago. Other posters were informed on 1/10 that the interview would be on the 25th, IOWs 4 days from tomorrow. I know when DS got his interview notification a few years back he was given 2 weeks notice. Burr did it much earlier back than, but still considered late (1st week of Jan for interviews). This yr. Burr is pushing it back to the last minute. His deadline will be required to be submitted to the SAS within 6 days of the interview.
If Burr stays true to form he usually interviews about 15-20 candidates per slate. It is not a given that you will get the non, but the odds are not against you compared to some other MOCs that interview.
I am assuming you are concerned more about your friends because if it was about you alone, why would Burr interview you? You have a principal nom to the only SA you are applying for, thus an automatic appointment. Hagan's IMPO was a waste of a slot on her slate because you have a principal, unless when offered a nom you didn't have the principal yet. Burr's office may feel it is a waste of time to interview since you are a definite IN if your are 3 Q, and if you are not, you won't get in with his nom either.