To those concerned about the issue of land usage: Monoterpenoids like limonene are great candidates for heterologous expression in bacteria, yeasts and even microalgae. As such the land usage issue is not as big a concern. If one uses microalgae you can even retain the many upsides of photosynthetic organism instead of the costly feeding of other microbes. It's still not at the level of commercial viability afaik, but the research in that area is promising.