It has been confirmed in discussions at the events in the fall that it will be the old Amex popup space (both platinum and centurion areas combined).

They’ve also talked a bit about their goal to locate as much flights as possible over towards the E&F piers. That being said ARN gate allocation is going to be crowded in the new few years with the apron/gate upgrades. Many more bus gates and C gates should be expected overall. I think this is also the biggest challenge in getting AF/KLM over to T5 as well. No great trades at the moment…