pg_ctl promote wait

It would be nice if pg_ctl promote supported the -w (wait) option.

How could pg_ctl determine when the promotion has finished?

We could query pg_is_in_recovery(), but that would require database
access, which we got rid of in pg_ctl.

We could check when recovery.conf is gone or recovery.done appears.
This could work, but I think some people are trying to get rid of these
files, so building a feature on that might be a problem?  (I think the
latest news on that was that the files might be different in this
hypothetical future but there would still be a file to prevent
re-recovery on restart.)

Other ideas?