Vertical farming, the best solution to support an ever growing population or just a scam?
IMHO it has a lot of potential but not being able to grow grains really is something that should be tackled sooner rather than later. But I could see this being used by self sustaining communities to provide lots of food while using very little space. And it's technically more environmentally friendly than just using vast stretches of land to produce the same amount of food.
While I totally agree with you, that cows have a slim potential to generate a calorie plus by eating exclusively from otherwise unsuitable land, I would argue that it will be unnecessary in most cases.
From an ethical standpoint, I must disagree with you as there is no justification to exploit animals if there are alternatives.