DEFAULT in <set clause list>

Folks,

While browsing through the SQL spec (200x draft), I noticed the
following:

<set clause list> (the list of SET expressions in an UPDATE statement;
section 14.12) allows a <contextually typed value specification> on the
right-hand side of SET assignments. One of the possibilities for a
<contextually typed value specification> is DEFAULT (section 6.5).

In other words, this syntax should be legal:

UPDATE sometable SET somecolumn = DEFAULT;

but it doesn't appear to be implemented as of CVS tip.

Any comments?

Cheers,

Neil