I see your concerns. I think we can't avoid using our land. The alternative would be not existing. Also we have to agree that most people demand a degree of consumerism that puts a strain on the resources we have. That's the reality we face. Paper is a very necessary good and probably will be forever. The production of paper is resource intensive. Removing lignin would reduce our demand of resources.
I don't see big poplar forests with the whole purpose of harvesting cellulose as that problematic if we keep in mind that this also gives more space for habitats we have to protect.What this research promises is that we can make the best of what we have because that is all we have left after we ravaged the planet and are not willing to stop that.