I know I may be in a majority but I would much prefer BA stay at T3. It’s a quicker taxi to and from the runway and there is a proper and fast domestic arrivals channel. I personally like the current security set up where you avoid schleping through a duty free shop on the way to the gate and it’s also close to the boarding gate, as is the lounge. I appreciate that would change when security and check in for T3 moves to T1 but I would still take it for the better taxi and arrivals arrangements.