So looking at this, assuming I'm QF LTG, and can easily make AA EXP (which I can), the pros and cons:
PROS:
8 AA SWUs (great for heading to Europe if you're willing to fly QF in Y to LA or similar - would use often)
Unlimited Domestic Upgrades in the USA (I would use this often)
Better AAward earn/burn
AA Flagship Checkin (reserved for AA EXP, not other OWE, but very few airports anyway so not really worried)
CONS:
Lose DOM J/QF First Class lounge access when flying JQ
Lose AA Flagship Lounge Access at LAX/ORD/JFK/MIA when flying domestically in the USA.
Lose access to QF Premium phoneline (can be the difference between 2-3 minutes vs 30+ minutes on the phone when there are IRROPs)
Might affect my run to QF Lifetime WP if it is offered in the future.
UNCHANGED:
Access to any lounges when flying any airline other than JQ.
Won't ever make WP1 nor AA Concierge Key, so no point in attacking either of those.
All in all, for the few times I'm in the Flagship Lounges, or on a JQ flight, it wouldn't seem like a bad deal. I would certainly miss the QF Premium Phoneline - being answered quickly is a massive boon!
More things to consider ahead of the LTG in a couple of years.