This is very interesting.  Generators are a powerful construct, and will ease the translation of code from languages like Javascript and Python.

One suggestion: in the Rationale section, explain why it's a good idea to provide generators in Scheme since they're so similar to streams.  It would be especially good to list specific use cases in which code is more easily expressed as generators than as streams, or in which generator-based code is more efficient than streams-based code.  This will be especially helpful for people new to Scheme.