This is very good news, I'm really tired of how bad Skype's quality has gotten. WhatsApp's voice calls, on the other hand, are almost always crystal clear, often better than even phone calls.
It's an extra link in the chain, meaning another potential bottleneck and added latency.
EUROPE TO US, EUROPE TO LATIN AMERICA, LATIN AMERICA - EUROPE ASIA TO EUROPE
All without latency.
I doubt that adding video calls to a chat app requires a featuritis diagnosis.
Email likely won't be an eventuality in this case.
They were (are) some of the best at working with WebRTC.
Edit: I would put more stock on Appear.in. They also have some of the best people, and they have recently launched a monetization plan (I was worried about that part)