Hi, I'm the author, I'm also a Ruby core committer, and yes I'm aware of Guilds. The are a model for parallelism and don't really affect concurrency at all. At best, they provide a 3rd option on top of processes/threads/guilds.
Guilds felt omitted in your post since they (should) address one of the points you make about the usability/ergonomics of existing Ruby APIs for managing non-sequential execution.
But it’s definitely a bit early to tell what Guilds will actually look like as a final product.
