Ozflier, maybe your biggest problem is your April 2022 timeframe. That's just too optimistic because many airlines appear to be factoring in a return to normal services from 1/7/22. After that date I have found J availability good for the flights that have been released. Since you mentioned Iceland maybe my experience will be of interest to you.
I have partially booked a 3 month 318K award for Mrs V and myself commencing at the end of July next year. 5 stops, 16 sectors and 53,000km. We will visit family in JNB first (to see our newest granddaughter for the first time). Still waiting for SYD - JNB availability because we don't have status but J seats don't appear likely to be a problem. What I have booked is JNB - LHR (transit) - KEF (stop) with BA. (FWIW, I had intended to go JNB - DOH - ARN but QR didn't have availability for a couple of weeks either side of the dates we wanted). Maybe flying to Iceland via SYD, JNB and LHR to KEF would be an option for you since availability through Asia or DOH is problematic especially because QR isn't even listing revenue fares out of any Australian capital city for next year yet.
Also I would add that the UK airport taxes are only a problem for long haul departures originating from LHR etc. If you are transiting London you will avoid them. (We will be having 2 transits and a stopover in LHR and will avoid the departure taxes by buying a cash fare across the Channel to BRU for a few days, which means we actually commence our trip home from there rather than the UK).
After 2 weeks in Iceland, I have already booked to then fly KEF - HEL - ARN in J with AY - so you're mistaken in thinking that AY no longer flies the HEL - KEF - HEL route. Even better, there's no waiting till 60 days before travel to get those J seats - there's plenty available now. I was able to book 5 flights online to start our itinerary, all in J, and it was all confirmed and ticketed within 30 minutes.
We will spend 5 weeks touring Scandinavia (including a cruise up the Norwegian coast), with 5 cheap short duration Y cash flights. From CPH we will re-commence the OW award and have time in PMI and NCE, for which I have seen plenty of J awards for BA flights.
No need to transfer from HND to NRT - Plenty of JL J availability for SYD - HND - HEL and HEL - HND - SYD (but you may not find the transit time to your liking and you may prefer to fly into a more central European city). AY flies the HND - HEL route too but I haven't seen any of their J awards for that, which is a shame because the HND transit times are a lot shorter than taking the 2 JL flights.
Overall, I have been pleasantly surprised at the supply of J award seats so if you can delay your trip by a few months you may be pleasantly surprised too. One last comment: Iceland in April isn't ideal - we intend to self drive and I found that travel conditions in August are much better because it's still summer and all roads will be open. That won't be the case in April.