I believe that if addon provided a hub, it would get mined by our collect* methods. However, I've never tested it so I cannot tell if it really works and what it does with the order. It's really not recommended, but we may get to the point somebody explains us they need something like that.
I'll go further and suggest that if we do currently allow adding hubs, we then disable that. What point would extra hubs have? Either stuff needs to be done before installation or during/post installation. Anything else we've got covered with standalone spokes. I don't really want to allow overly flexible customization, as that's how we end up in problems like too many installation methods and the current driver disk mess.
- Chris