If the straps pulled up from the outside inline with the axle spindles and you had a cross bar between the straps with a keel rest and pads (like a boat cradle) you would eliminate the torque effect I think. The bars from the cradle could be pinned to the main frame for travel helping to eliminate torsional twist on the main beams. You could also lower the front and back straps independently and put the boat in to the water level. Where's my sketch pad?You might need a cross bar above the deck if the frame is not built like a bridge.
The automated hitch extension would be a piece of cake to build. With a remote control you could back the vehicle hitch to the edge of the water climb onto the boat and remotely put the trailer in the water. This would be great for single handed launching when you don't have a dock next to the ramp. I don't normally ask for input on my designs but this is really helping me to open my mind