Bringing forward Nimrod OSD was muted several months ago when the costs of getting the frames to an acceptable airworthiness condition became apparent. It was considered to be too expensive to fix. This is purely about trading off capability against cost. On paper there is a capability gap for a few short years, but there is a BIG risk in this decision. I am already hearing of problems with MRA4, (related to H-C). This is a calculated gamble, only time will tell if it is the correct decision. I and I suspect many others, would rather have seen the money spent on the existing airframe, which is already safer than it has been for many years.
Must be fairly desperate times in the Puzzle Palace...