returning clause and source columns

Hi

Related to this post: http://dba.stackexchange.com/q/50693/1396

Would it be a major change to allow the `returning` clause of `insert` to
return values that are *not* inserted? It seems you can already do so for
literals (and perhaps that should be made explicit in the docs here:
http://www.postgresql.org/docs/9.3/static/sql-insert.html#VARIABLELIST)

For example:

insert into t1(id) select id from t2 returning *, t2.foo;

Kindest regards

Jack