Here's an interesting and promising interview with an Italian researcher ...
... that is familiar with PLX and sees a lot of potential for drug development in many areas. The article is two pages long and you may need to use google translate, but below is one excerpt from the second page:
What drugs you could do with this technique or the whole plant?
Important examples of successful production in the laboratory are antibodies, antigens for vaccination, many enzymes, components of the blood and breast milk. Some proteins have need of specific cellular components that may be difficult to obtain in plant cells. But certainly similar problems are present in any other type of cell or organism used. In general, the recombinant human proteins produced in plants have activity equivalent or even better than those produced in a more expensive in bacteria or other microorganisms.