option one would help torsionaly in a turn, not to much in the longitudinal (tip to tail) direction.
i would be concerned with the stress concentrations where the wood stops.
If i were to do any reinforcing i would add carbon tape from the rear binding out to the swallow tips on the tail ( reverse V pattern )
I personally wouldnt be that worried about the tail flex. A normal tail of a board rolls up yours is now flat. Many boards have rocker in the tail and perform fine. My pow boards of choice is a lib snowmullet and k2 gyrator which both have rockered tails.
I know i' overthinking this, but thats a fun part of it for me. Lol
try it first, modify later. This board will ride different than others thats the point, adapt your riding style to fit the board.
Torsional flex is what concerns me a little, let face it even if i plan to go on a powder day...sometimes, theres not as much snow as expected at the moutain so I would like the board to be rideable in a broad range of conditions.