Honestly, this seems like a solution looking for a problem. We already have a lot of agricultural space available and in use. We just use that space very inefficiently to actually produce food. There are huge benefits to be gained from switching to sustainable farming, and probably a largely vegan diet too (just based on Ressource use alone). Once farming is focused on producing food and preserving nature, instead of creating profit we can look to further improvements. Even hydroponics or mixed use gardens are likely a better next step here. There simply isn't a need to cram our food production onto a wall yet, especially if that requires costly infrastructure made of difficult to recycle materials.