Even if the goal of getting Ruby 3 to be 3x faster than Ruby 2 on a typical Rails app is reached, it would be far from the 17x speedup they got by moving to Rust.
I guess it depends. TruffleRuby could be 200x faster in some benchmarks. So it is not that 17x speedup is an impossible task. It just needs some testing to be sure.
Obviously, performance is important; however, there is huge difference in the engineering cost of splitting your codebase into 2 languages and upgrading a language version in both the short term and long term. A 17x speed up in code doesn't guarantee a 17x speed up on future iterations of their product.
I am not saying they made the wrong choice; it seems like what they chose worked for their use case. It could have been the case that 2.6 didn't work for their needs, but I think it's still worth an investigation.
A naive perspective: Crystal is still a baby with a relatively tiny userbase, so I'm willing to bet there's plenty of Ruby gems that they use that don't exist in Crystal.
