COPY (query) TO file

Tom had posted a question about file compression with copy. I thought
about it, and I want to through this out and see if anyone things it is a
good idea.

Currently, the COPY command only copies a table, what if it could operate
with a query, as:

COPY (select * from mytable where foo='bar') as BAR TO stdout

I have no idea if it is doable, but I can see uses for replication

psql -h source mydb -c "COPY (select * from mytable where ID > xxxxx) as
mytable TO STDOUT" | psql -h target mydb -c "COPY mytable FROM stdin"