I think that moving out of T1 is the best move CX could have made, and T4 isn't even open so judgement should be reserved until at least the end of November once the kinks are worked out.
Side note T5 is set to finish in the late 2020s (so say 2027-2029), that's 10 years away at least. There is nothing stopping CX from moving to those terminals if they want to and can negotiate it. Besides T5 is more like the satellite terminals in HKG because of their position.