Edward Shishkin, the last main active developer to Reiser4 that's still maintaining things, released Reiser4 for the Linux 4.2.1 and 4.2.2 kernels last week. With the Linux 4.2 Reiser4 port it's just working around changes within the mainline Linux kernel while Reiser4 didn't see any new feature additions. Although with the Reiser4 port to Linux 4.1.5 last month, it looks like meta-data checksums were added to Reiser4.
Those wanting to grab the patches for Reiser4 on the Linux 4.x kernels can find the patches on SourceForge. The ReiserFS mailing list sadly remains void of any major feature discussions. The last communications about any mainlining of Reiser4 indicated that there were no plans until any major Linux company is willing to get behind and support this file-system, which there's been no signs of with most sticking to EXT4 or XFS and looking forward to Btrfs and F2FS in the future.