Since the only thing I've never known NP to delay timing on is a YouTube or radio interview, either some more news is on the horizon that he would like to share, or it's possible something just came up more important (ie Family matter, big meeting that can't be moved etc).
Thank you LaundryMoney.
You are absolutely right on that "something just came up more important", and he is just too busy with other priorities. I'd give this 90% chance.
I doubt there is NOT more than 35% chance of announcing the BLA on that day.