Somebody on Reddit was curious: how are the Ruby folks doing on Ruby 3x3? This answer may be useful to some of you out there as well... (Please note that I don't decide this stuff, but I do keep track of it fairly closely.)
The main announced thrusts of Ruby 3 are performance, concurrency and typing.
For performance, the work is primarily occurring in the normal Ruby trunk. Matz has announced that he wants Ruby 3 to be three times as fast as Ruby 2.0.0, and there has been great progress in that direction. Rails Ruby Bench is (surprise) a benchmark checking Ruby's performance using a big highly-concurrent Rails app. You can see the results on this engineering blog, thanks to Appfolio, who sponsor my Ruby 3 work. You can also look up optcarrot, which is the other major Ruby 3 benchmark. Mine is Rails-based, while optcarrot is primarily a CPU benchmark. On the Rails-based benchmark, Ruby 2.5.0 head-of-master is around 165% of the speed of Ruby 2.0.0, so progress isn't bad. The optcarrot numbers are also quite good.
In addition to normal "let's make slow things faster" performance work, there are the two JIT branches mentioned below - Takashi and Vlad have been working independently and together, and at this point it looks like Vlad's JIT implementation is likely to make it into Ruby 3 in around a year, if nothing changes (this is not a formal announcement, just a wild prediction, do not take it as guaranteed ;-) )... Though possibly without his changes to convert Ruby's stack-based VM into a register-based VM. The register-based version is faster, but less compatible and would need more stability testing. Takashi's YARV-MJIT branch is just the JIT without the register-based VM changes.
For more Ruby 3 progress, I highly recommend looking up RubyKaigi 2017 videos on YouTube and RubyConf 2017 on ConFreaks. They record all the major Ruby conferences, and a lot of the proposals and status updates have been happening as conference talks. The talks are all available entirely free, though some of the RubyKaigi talks are in Japanese :-(
In particular, Takashi Kokubun gave a *great* YARV-MJIT talk this year at RubyConf, just a few weeks ago. There were several different gradual-typing talks at RubyKaigi and one by Soutaro Matsumoto (no relation) at RubyConf.
Unfortunately, the Guilds-based concurrency stuff isn't in Ruby trunk. There have been a few good blog posts about it (I like this one.) Koichi Sasada, the author of the current Ruby VM, is currently working on it. My understanding is that there's not a current version being shared around. I don't have a good feel for where that's at.
As of RubyKaigi, Matz has said he's not wild about any of the existing gradual-typing proposals, so we're basically at "still figuring out the spec" on Ruby 3 changes to the type system. We've had some on-paper proposals and some early implementations, but nothing is currently close to getting included as a standard part of the language.
And those are the big three, as far as Ruby 3 goes: performance, concurrency, typing. There are some small things "in orbit" around them like static analysis proposals for typing and benchmarking for performance.
But that's basically where things stand.