• Apple's Plan: Moving away from kernel extensions and running more in user space, recruiting volunteers, especially from eligible file systems. Sequoia offers new APIs including user space file system support.
• Developer Documentation: A new section in Apple's developer documentation for the FSKit framework is emerging. Currently, only the contents are listed without explanations.
• Release Details: The whole FSKit framework is claimed to be a beta-release for macOS 15, but most if not all of it is available in macOS 14.0 and later. Apple has used FSKit as a Private Framework since macOS 14.0. In MSDOSFS open source on Github, its code was last modified nine months ago. The msdosfs.kext kernel extension is still included in macOS up to 14.5 with no changes.
• Documentation: The closest documentation is in macOS developer release notes. Ventura 13.0 reported a change to msdos and exfat file systems with no details. Sonoma 14.0 was more explicit about the change, with file systems now provided by user-space services instead of kernel extensions. Maybe the remaining kernel extension is vestigial.
• Transition: Apple is transitioning secondary file systems away from kernel extensions to user space. MSDOS file system started in macOS Ventura 13.0 and completed in Sonoma 14.0. Others can implement support with limited features in 14.0 and full support in Sequoia.
• Implementation: FSKit is essentially undocumented currently, and Apple doesn't mention how to make it work as a system instead of a kernel extension. macFUSE is mentioned as an option.