With regards to using plants to grow medicines in space - I think that it it makes more sense to use microorganisms for this. So I am trying to reason whether there is a reason why one would prefer to use a plant.

Perhaps since plants already have more complex bio-synthetic machinery to create secondary metabolites than bacteria, fewer genes would have to be added to produce the target molecule. Fungi also have a lot of powerful systems already built-in. I think that it will be a case-by-case basis, a specific target molecule will be easier to produce using a specific organism.

So a space medicine farm could end up being interestingly diverse… For example, goats have been genetically engineered to produce milk that contains spider silk.

Eventually I do think that metabolic engineering could move far enough that it will be possible to engineer whatever machinery you want into easier to grow microorganisms. Then we will just grow everything in flasks in shakers and bioreactors.