I agree fully that it is not a permanent solution, nor a possibility to replace all food with a single different one be that seaweed, insects farming, hydroponics, or other non-traditional forms. I do however want to highlight that food is cultural thus peacefully changeable. We can extend the window much further than just what currently exploitation of farm land do. Aquaculture is just one of the more likely approaches since it is already part of some cultures, although quite small ones in term of populations.

It is an interesting question if a new world war is more likely than a major cultural change in our diet.