But Linux distributions still cannot officially use it… sort of?
Samsung added support for exFAT on Linux, in kernel, with one of their tablets. At some point code was leaked on GitHub. At some other point the Software Freedom Conservancy determined certain GPL-dependent modifications were published in binary form alone. Eventually Samsung properly released their source code under the GNU General Public License (GPL).
I am still unclear about how Samsung was allowed to do so, however. Copyright was never the main concern with exFAT but rather the patents Microsoft holds over the file system. The GPL mandates that code it covers must come with a non-exclusive worldwide and royalty-free license for applicable patents except under certain conditions. I would be curious how this license was accomplished unless Microsoft granted Samsung a patent license prior to March 28, 2007 (or some loophole like that).
I understand how people might be sympathetic to Microsoft and others asserting software patents because they are a for-profit business but that does not apply everywhere. You need to be careful when you apply a license to something as upstream as a file system or a kernel as everything downstream relies upon your decision.
Just imagine if you were separated from the contents of your SDXC card because, somehow, this patent found its way into the portfolio of a troll firm?
Current implementations of the file system are in user space until Samsung's in-kernel module. The Software Freedom Conservancy praised Samsung — not only for their source code contribution — but also for how open and public their response was.