That's an interesting use case, but the only time you're actually using Google Hangouts is when you're already in a conversation with someone, so I imagine that's not where most people would go when they want to schedule a call with someone.

When I think about scheduling, I immediately think about Google Calendar or Google+ Events, because that's where I would go to schedule any sort of event (with a video call or otherwise). Both of those places support adding a Hangouts video chat to an event.