DSSSL does not and therefore Chicken doesn't either. S7 doesn't, Gauche doesn't, Gambit doesn't. Guile does. I think that's enough for us to reject it.
One more unresolved problem is whether 177 should support
"allow-other-keys". It would be useful in making wrapper procedures that
can pass unknown keywords on to another procedure.
I didn't check whether all the current Scheme implementations with
native keywords support allow-other-keys. I suspect some of them don't;
in that case the feature has to be left out of 177.