I think it will be as expensive to app to convert UUID to standard
format, as it would be too postgrsql.
But if psql does it - everyone would expect it to do it right. You
can't possibly detect all forms of screwed up design, and expect
application to pick it up.
All I say, is I think it would be better to be conservative in this
case. And funny enough, I only replied to that message - because I
know something about trying to compensate for non standard types, and
I've seen that discussion quite few times around here in the past.
Just a friendly opinion.