V4 protocol, extensible?

In another thread I was made aware that current protocol may not be
easily extensible (if at all), and so the backend-data a certain driver
needs may not be so easily added.

http://www.postgresql.org/docs/current/static/protocol-message-formats.html

So if there is not already a roadmap for this, one idea may be to use
some kind of key-length-value type encoding, which seems to be one of
the most accepted formats for extensible streams (though I am by no
means an expert). Names could just be ints/oids and not chars to their
real name.

Just wanted to see if anyone had any thoughts on this, or if my
presumption that metatdata in the current V3 cannot be easily added too,
is wrong.

Thank you,
Ken