Early studies suggest that diverse silvopasture can be just as productive as monocropped grain, but it means a major change in diets and the food production system world wide. It means less meat (but not no meat) and a diet focused more heavily on fruit and nuts rather than grains. This is a huge cultural shift and also a huge economic one, since much of the food industry is completely dependent on value added processed grains.
But if we start looking at how chesnuts, hazelnuts, walnuts, and acorns could be stored and processed into a greater variety of foods, then we can start the move towards agricultures that are just as productive and way healthier for the environment.
No-till, poly cropped grain production (corn, beans, and squash in the same field) can also act as a carbon sink, but it doesn't lend itself to mechanized harvest right now, so it would need to happen to a smaller degree.
Which basically means it's not going to happen. There are lots of ways to fix climate change that involve large scale changes to human behavior and habits. They're not viable because nobody is going to do them. The reason devices like this are valuable is that they promise to allow us to keep doing the things we're doing and stop or slow down climate change.
Based on your usage of "much" in this sentence and then detailed plans around crops, there must be some studies that quantify this to some degree. However, in my searching, I haven't found any such studies. Do you happen to have any favorites? Perhaps I need to dig into some of the IPCC references on land usage next.
Incidentally, it is my understanding that coal use is already declining rapidly. In many cases, it is being replaced by natural gas: certainly not ideal, but better.