it’s not about selling it as a product. it’s about determining what molecular pathways are interchangeable between plants, fungus and animals.

They synthesize a ton of stuff with bacteria these days! Bacteria are really good at making almost any compound you can think of! I think with this study, part of the novelty was harnessing multiple molecular pathways in animals, fungus and plants, all with with analogs in a single plant. A lot of the paper was about discussing the different enzymes available in the plant, like a kind of toolkit that just had to be tweaked

Yes, this is basic research, which generally starts with common model organisms that many labs have access to. This increases reproducibility of the early results. The study mentions expression of the relevant genes and proteins in the buds as well, and also calls out one of the pathways in tomato, so perhaps the next step could be to test it in other nightshades and their fruit

They used an Australian wild tobacco that is widely used in genetic research, so not the American domesticated tobacco https://en.wikipedia.org/wiki/Nicotiana_benthamiana