I think it’s a great feature that has the potential to bring a solid concurrency pattern to Ruby. I think that it is quite amazing that Ruby adopted the actor model: this has the potential to make Ruby even better than it already was.
Is this making Ruby preferable to Elixir/Erlang for concurrency? Most likely not, because of the issues with mutability mentioned above, and the lack of a VM designed from the beginning for safe concurrency. But I believe that’s not the point: this feature makes Ruby better, and applicable to more problems than it used to be.
I think about this as beneficial “cross-pollination” between languages, not as a competition.
As an engineer that loves both Ruby and Elixir, this feature makes me happy, as it expands the creative space of my favorite tools. If I am designing specifically for concurrency, I will still reach for Elixir. But in a project that fits Ruby better, this makes it possible to introduce concurrency where needed, using a pattern I like.
As for the GenServer implementation, I look at it more as an example to understand how Ractors work, than as a piece of code I would introduce in a real app. It wouldn’t make real sense to port exactly OTP GenServers to Ractors, as the underlying system is different. In Ruby, I would use the actor model idiomatically, without trying to mimic OTP too closely.