I suggest dropping hash-table-ref/default and hash-table-update!/default.
These gain little in convenience, and don't serve any aim of the SRFI so far
as I can tell.

Also note that the current specification is not correct:

    Procedure: hash-table-ref/default hash-table key default -> value

    Equivalent to (hash-table-ref hash-table key (lambda () default)).

Consider default = ((lambda (x) (x x)) (lambda (x) (x x))).  The program
(hash-table-ref ht k (lambda () default)) diverges only when the key k is not
found.  The program (hash-table-ref/default ht k default) always diverges.

David