Ch 9 from the flight deck has been enabled and operable on maybe 1 UA flight in 3 that I've taken over the few months. (Excluding UX flights obviously.)

It has been disabled by the flight crew (playing the music program) on about half the flights, and the in-seat audio has been inop on the remainder - mostly on the ex-sh*ttle 733s or 735s that have seen much better days.

For me, Ch9 could be a huge selling point - it certainly makes me overlook the lousy interior conditions of the aircraft I fly regionally compared to, say, AS. Unfortunately, it's so inconsistently available recently that I no longer factor it into my travel booking decisions.