Very low probability of overbooking and even lower probability to get to a lowly OWS after they have gone through the long list of JAL elites.
Im a JAL JGC and even that usually puts me behind 20 or so JGPs and Diamonds (literally on all of my many flights).
So, unless you are willing to pay the fare difference to upgrade to Biz, or the premium economy upsell at the counter, just forget about it.