The implementation of converting now() to CURRENT_TIMESTAMP seems like an underdocumented kluge, too.
I'm very late to the party, but it seems to me that this effort is describing a small subset of what "routine mapping" seems to be for: defining function calls that can be pushed down to the foreign server, and the analogous function on the foreign side. We may want to consider implementing just enough of CREATE ROUTINE MAPPING and DROP ROUTINE MAPPING to support these specific fixed functions.
