My understanding is that the very low offset values will only be used to properly surveyed fixed platforms, and the actual offset distances will vary with the approach direction (for the reasons highlighted above) and will be published on the OSAP/ARA chart. There is no suggestion that the pilots will leave it to random guess work, and mobile installations will need higher offsets.
Regarding the point about landing and decoupling, the Flight Director ends up in velocity and Radalt hold in the final stages of the approach, with a 30kts ground speed. The intent is to not decouple immediately, but to use the cyclic beep switch to adjust the velocity vector's direction and speed towards the deck. Decoupling can take place at a very late stage. It's effectively an adaptation of the SAR AFCS. I've tried it in the simulator and it's very impressive.
I think one of the greatest benefits will be for night approaches and DVE conditions - other than simple cloud break - as that is where most of the offshore accidents have occurred in the last 20+ years.
There's just that small question of cost now
