If "_" is used, it should not be bound by this SRFI to a new transformer but should imported and reexported from (scheme base), so that "(import (scheme base) (srfi 156))" works (and would detect if the meaning of "_" in the importing program is different from either the meaning of "_" in (scheme base) or (srfi 156)).
That's true. I was just wondering about a compelling reason for many to use this new syntax.
I agree with this point. This is also more consistent with the use of "<>" in SRFI 26. The whole use of "_" as a placeholder, however, is not consistent with the prior use of "_" in the R7RS, where it does not bind any variables but ignores arguments. (Which would speak for "<>" of SRFI 26.)
One more point:
9) While the addition of "isnt" is nice, having another primitive to turn the arguments around can also be very helpful. So "(isnt x < y)" is "(is x >= y)". Do you have an idea for naming a syntax S such that "(S x < y)" is (is x > y)", that is "(is y < x)"?