In terms of the shared check-in area, I assume that BA staff can check you in for an AA flight / itinerary and vice versa? Or if you're flying BA do you have to wait for a BA agent to be available?

Thanks Genius1 for an excellent report. I rarely fly through JFK so I think it'll be some time before I get to enjoy (suffer?) the shared T8 experience and, hopefully, the teething issues will be resolved by then. As you say, it's so frustrating that the new lounges have failed to incorporate the best of both airlines' previous lounges and have ended up with an unsatisfactory "dumbing down" of the premium experience.