This SRFI is a tour de force. Nice job.
I have just a few small comments:
* In the description of `regexp-fold', in "...calls finish with the same argument," the word "argument" should be plural.
* In the paragraph describing `rx-match-submatch', the sentence beginning "if an integer outside..." is confusing. I suggest changing it to "If passed an integer outside the range of matches, or a symbol which does not correspond to a named submatch of the pattern, it is an error."
* The phrase "desirable to want to" should just be "desirable to."
* I agree that <- would be a better choice than =>. Perhaps now is the time to make the change before SRFI 115 is set in stone. There's a great story from the original author of Make. He said that he decided early on that he couldn't reverse the decision to make SPC and TAB have different meanings -- a terrible decision -- because he already had ten users!