The company with half the top Phds and best engineers in the world and billions in profit every quarter is unable to create an open extension to XMPP to accomplish those and fallback gracefully if it's not supported? You really believe that?
You could assemble a team of 30 random HN posters and they would be able to do that.
So, I think they could do it, if and only if they wanted to. But they didn't and they themselves said it was because they didn't want to be open.
The hypothesized "video chat" protocol extension to XMPP already exists and it's called Jingle. FOSS client support isn't great, but it is progressing. So if this service isn't open to FOSS clients, that's more an issue of strategy than resources. (And indeed, the decision might change in future and be attributed to improved FOSS client performance.) If the service is indeed closed, however, they probably ought to update this page:
You could assemble a team of 30 random HN posters and they would be able to do that.
So, I think they could do it, if and only if they wanted to. But they didn't and they themselves said it was because they didn't want to be open.