Taking MIT code and re-licensing it under the GPL will cause a huge uproar:

http://undeadly.org/cgi?action=article&sid=20070913014315

I'm not sure that is even legal.

I didn't mean re-licensing it - the parts that are under MIT stay under MIT, but the patches on it have a different license. That is completely legal and license doesn't forbid this. (ianal, yadda yadda...)

A similar thing happened to OpenOffice / LibreOffice: [0]

> OpenOffice uses the Apache License, whereas LibreOffice uses a dual LGPLv3/Mozilla Public license.

> For some legal reasons, then, anything OpenOffice does can be incorporated into LibreOffice, the terms of the license permit that. But if LibreOffice adds something, take font embedding, for example, OpenOffice can’t legally incorporate that code.

[0] https://hackaday.com/2020/11/02/openoffice-or-libreoffice-a-...

It's doable if you can get OK from every single copyright owner of the source files.

LLVM did it. Switching from "University of Illinois/NCSA" to "APL 2.0".

But not without some big discussions.