AIUI, we're not committed yet, but are certainly on the vinegar strokes / got the Jesters toes......
It will probably be too late to get cat n trap into QE before her first refit, but the possibility remains for PoW to enter service fitted for Dave C - particularly given that QE will still be operating GR9 until 2017/2018, which is broadly the IOC for Dave B. Switching to Dave C might knock that back a bit, but ain't a show-stopper yet.
Either way, decision must be made before the end FY at latest.