Just to update.
I decided to cancel as my SYD/TYO/LHR/TYO/SYD already had virtually no biz class C & D availability for the required revised return date TYO/SYD (late Jan, I guess due ski season & end Aussie school break) so JAL's insistence that I'd have to wait until after the outbound in June to re-book was looking expensive if I would need to upgrade to full J fare or worse, not be able to use the return at all.

So I decided to cancel as BA had released "I" availability on my required dates SYD/LHR via SIN at a similar price and that avoided the 2hr JAL Alaska detour outbound.

Bad news was that cancellation apparently couldn't be done online (Stone Age website?) and took 62 minutes on phone with call centre from Oz just to cancel 2 tickets. No problems raised as originally just simple online bookings (self and son on D fare and wife on C fare), but still unexplained huge musical interludes between which they repeatedly verified ticket/route details and then worked out refund (fare minus the A$400 cancellation fee, which had taken me two seconds to work out) for each of the reservations . Incredible - I did wonder during this call whether they deliberately make it difficult to cancel like the cable TV co's? Good news was that despite their warning that the refund would take 2 or 3 months to process, the $21k was back in my Amex card account within 24hrs.