Good idea
I think deferring the move is a good idea. I've been through T5 on 3 different trips and each time the experience has been positive. I've been on time through a nice modern building which beats T1 hands down. You can see there is less congestion on the airfield and the service roads - it has been well designed.
It is also totally clear that T5 building isn't finished, there are temporary doors, lifts not working, missing hand rails etc. That is down to the BAA - they've haven't finished the building but are greedy enough to want occupancy and rents.
BA delaying the longhaul move is sensible, it gives more time to train staff from T4 so lessons are learnt and applied before the move.
BMI are just looking for publicity. T1 is now nice and quiet so they can run their operation with less congestion. BA has vacated so Star alliance can move on scheduled. If anything BMI has gained a little from some PAX moving from BA due to disruption.
I know there are plenty of critcs for T5, but my experiences have been good.
CB