An update to my drawing:
{Image updated in message 75 to show SmartThings}
I wanted to have the diagram show that some products and tools work just fine on both hubs and don't benefit from a third hub.... Which comes to a question...
How many people around here are using more than one hub and find Link to Hub restrictions are impacting them? That's the group of people that should explore HubConnect.
@srwhite is close to releasing it, he says. There's not a lot of learning curve to it. It works as expected. If there's adequate interest, I'll put together a how-to with screen caps.