It was Edward Shishkin that told us in 2009 that we could see Reiser4 in the mainline Linux kernel in 2010. Edward's reasoning for this 2010 target was first to allow time to publish a design document about Reiser4, such as for USENIX 2010, to gain some independent expert review. Edward is the developer that basically took over leading the Reiser4 development after the founder of ReiserFS/Reiser4, Hans Reiser, was convicted of murdering his wife.
Curious as to what the state of Reiser4 is now at since there's been no large public debate in recent times about pushing it into the mainline kernel, we reached out to Edward again. Below is the email received this morning from Edward Shishkin concerning Reiser4 and its aspirations to go into the mainline tree.
I don't see any technical obstacles for Reiser4 inclusion. There are only organisation ones: I don't think it will be accepted without support from some vendor.
One company might have an interest in developing Reiser4, as they said, however, there is no essential progress in this direction for now..
In other words, Reiser4 should basically be ready for the mainline Linux kernel but it'd be better off if some vendor wanting to utilize Reiser4 would get behind its development. This though may be a tough sell considering most distribution vendors are happily using the EXT4 file-system until the Btrfs file-system is ready for production, every-day use. Btrfs is viewed as being the next-generation Linux file-system and our performance test results and its feature-set have shown great promise and abilities compared to competitors like Oracle's ZFS file-system, which is also now available for Linux.
Until the point that Reiser4 makes it in the upstream kernel, one of the easier ways of utilizing this file-system besides applying the patches manually is to use one of the Zen Linux kernels. Last year we also published Reiser4 benchmarks comparing the file-system to EXT4 and Btrfs.