I really wish I can express my opinion in a video with my voice and good pictures~^^
Basically because although my country(Taiwan) is kinda famous for delicious foods, we also have some huge illegal food problems ...so I imagine there's an evil team who does such kinda thing in a Taiwan-based region .
In short~my evil team is a company that sells various food products, some of which can even be used to affect Nature~IV~EV~etc. On the surface it seems fine~but in my story~some severe side effects will appear gradually.
For example, you use certain item to change the nature of your Pokemon, and maybe at the time it's around LV50, a random confusion could happen when it battles.
I didn't play lots of fan games but I really don't want to deal with things like EV~IV~Nature in fan games. So I want to tie up stuff like genetically modified Berries or Ultra EV-enhancing items with the game as a story. Also kinda for the sake of irony. Although it's just me, I don't know if people will use such items when they actually receive some without thinking too much or not, however in the game your pokemon will be forced to eat this somehow anyway.