A few months ago at
http://archives.postgresql.org/pgsql-general/2006-11/msg01770.php the
notion of adding an "anyelement2" pseudotype was discussed. The context
was a compatibility SQL function to support Oracle's DECODE function.
Assuming this new pseudotype has not been added yet, I'm ready to look
into doing this myself, and I'd like a bit of shove in the right direction.