The high-profile Bcachefs was not merged into the mainline during the Linux 6.6 development cycle because Linus Torvalds still had concerns about it - it had not been reviewed by the "linux-next" staging area.
However, judging from the latest merging of the kernel, everyone sees hope of introducing a new file system driver in Linux 6.7.
Just last night, the Bcachefs filesystem driver was merged into the Linux-Next code tree as a loose testing area for experimental code hopefully into the "next" kernel cycle.
Bcachefs is a copy-on-write (CoW) file system derived from the Linux kernel's block cache Bcache. A few months ago, the Bcachefs patch set was officially submitted for review and is expected to be included in the kernel.
Developers hope to provide XFS/EXT4-like performance and features similar to Btrfs and ZFS. Its lead developer says that Bcachefs has "too many features to list" and "too many known bugs to list".
Bcachefs' Git repository has now been pulled into Linux-Next to allow more developers to focus on the code and all the automated build/test infrastructure used by various individuals and vendors to test these leading "-next" codes.
Additionally, putting Bcachefs into Linux-Next will allow for more build testing of the code in different environments, ideally catching any remaining bugs before the next Linux kernel merge window opens in two months.
See details: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/log/?qt=grep&q=bcachefs
Further reading