I would merge the two ideas: `write-unreadable` outputs "#<", a datum as if by `write`, and ">" in that order, and #< is required to signal an error satisfying read-error?. That's enough for a SRFI.
Marc N-W has made me see the light on #<...> so I can no longer recommend it. I can only accept it as an alternative for the sake of compatibility.
IMHO lexical syntax SRFIs should be standalone anyway; procedures and syntax are orthogonal concerns and mixing them causes problems for the community. But I don't expect to change anyone's mind.
