Where in the MIT license does it say you can't bar redistribution in your proprietary fork? That's obviously what everybody does when they use MIT code in their proprietary products? That's the whole point.
No, since most open source projects don't require you to sign over your copyright when you contribute. For these projects, you need the agreement of everybody that contributed to the project to change the license, since they own a part of the project. In the case of Node.js, Ryan required all contributors to sign over their copyrights, so he was free to do whatever he wanted with the code. That includes relicensing or selling it.
Well I am willing to bet you are wrong. It just doesn't make sense. By your logic my only insurance against some Open Source project going bad on me is that it has a variety of contributors, at least one of whom would not be willing to relicense. That would make OS licenses completely useless.