Tux3 is the file-system that warranted attention a few years prior as an open-source versioning file-system to succeed the Tux2 file-system that was challenged by licensing issues. While promising at first, Tux3 virtually disappeared for a few years time.
At the beginning of this year, Tux3 came back to life with results that promised to be competitive with the very common EXT4 file-system. Added shortly thereafter was Tux3 FSCK support but still, the file-system hasn't been merged.
When asked recently on the Linux kernel mailing list about whether Tux3 is still months later, Daniel Phillips of the project responded on the list.
Tux3 is not dead but there's plenty of activity happening to its source tree on GitHub. The most recent activity is from earlier in March. There's also a mailing list for Tux3.
In terms of why there isn't any major Tux3 news at the moment, Daniel responds, is that they're in the midst of developing the next-gen directory index. It looks like it may still be a while before Tux3 is called for mainline inclusion within the Linux kernel.