Having just recently returned from NRT on JQ24 ( NRT > MEL) I can confirm that the QF NRT lounge will be open for this flight.
At the reception, just like at many other QF Lounges, rules of eligible entry were visible & both Sapphire & Emerald QFF members are eligible to use this lounge for JQi flights.
I was travelling on a business max bundle & I was given a QF embossed invite to the lounge upon check in, which I found a nice touch as it had my name on it. You don't get these at other ports to the best of my knowledge when flying on JQi business max bundles.
Another observation I made at NRT was that Priority check in for business class passengers works very well at NRT for JQi passengers who were served immediately upon approaching the check in desk, jumping the large queue for economy passengers.