[Swannie]

My question isn't really about stabilising the platform, as others have mentioned that should be off the shelf marine tech.

But this isn't exactly landing a helicopter on a ship/platform. I'm expecting a rocket to be a fair bit heavier... as that weight comes down, unless it's perfectly on centre, you now have a large force acting to unbalance the platform. Whilst X-Y may be stabilised, the pitch and the yaw is going to be affected by that weight.