Context:
Permissive licenses (commonly referred to as "cuck licenses") like the MIT license allow others to modify your software and release it under an unfree license. Copyleft licenses (like the Gnu General Public License) mandate that all derivative works remain free.
Andrew Tanenbaum developed MINIX, a modular operating system kernel. Intel went ahead and used it to build Management Engine, arguably one of the most widespread and invasive pieces of malware in the world, without even as much as telling him. There's nothing Tanenbaum could do, since the MIT license allows this.
Erik Andersen is one of the developers of Busybox, a minimal implementation of that's suited for embedded systems. Many companies tried to steal his code and distribute it with their unfree products, but since it's protected under the GPL, Busybox developers were able to sue them and gain some money in the process.
Interestingly enough, Tanenbaum doesn't seem to mind what intel did. But there are some examples out there of people regretting releasing their work under a permissive license.
Only if they are still the only contributor. Once you have more contributors, it gets far tougher to change the licence.
Pretty sure that with a permissive license you can just change the license of future versions as you want. Ex. v1 MIT license with thousanda.of contributors, v2 Commercial license with contributions from anyone who agrees to contribute to the new version and license. (Anyone can fork v1 and start their own licensed project)
How does it work with contributors? Does absolutely everyone have to consent to having the license changed? If one of the contributors doesn't consent, can the maintainer "cut out" their contributions into a separate program and redistribute it as a plugin with the original license?
You can keep all the lines of those who didn't accept to the change with the original license, it will end up as a bad mix, but it's doable if the licenses are compatible
Very minor changes (like fixing typos in comments) aren't copyrightable, so these changes don't require approval. When LibreOffice was relicensed, IIRC they they had some cutoff regarding lines of code.