When we had our in-person YC interview way back in 2010 it was incredibly helpful to have time beforehand outside the interview room where we got to hang out with other hopeful founders and casually chat, learn about what they were doing, and talk about ourselves and our product a little.
Like a warmup, it helped to calm everyone's nerves and got us into a mode of talking confidently and happily before going in.
That moment before the interview was incredibly empowering to me as a first time founder because it was also my first exposure to a bunch of other people who seemed to be just like me: passionate about not only building products but also building companies (which at the time wasn't common at all in my social circles).
I think even if we had not gotten in that experience would have given us the confidence to continue forward as founders.
It's a shame if the video calls remove this opportunity for interviewees. I think a few startups are trying something like this, but it would be cool if there was a way for YC to let founders wait together in a virtual lobby of some kind where they can have casual conversations ahead of time, exchange contact info, etc.