Even if that is correct, if you really want to use VM, it is still better to modify a simple Ruby implementation like mruby/c or picoruby than to modify Crystal. I thought these used a common bytecode with mruby.
Have you read the long discussion in the thread presented by MistressRemilia? Aside from VM, incremental compilation is a feature that does not exist because it is difficult to achieve, even though many people want it.
Does the concept of compiled objects/libraries without type definitions exist in any other programming language?