Exotic in this case just means uncommon or rare in the wild, not expensive. Something like requiring both salt and aspartame would help prevent gene transfer in the wild (to related or unrelated strains) as well as making it unlikely to grow on its own.
I would love to have something like that, but unfortunately that’s a really hard problem in itself, so I’d likely only start working on it once the need arises
Presumably you're working on this as a technique for widespread use by other parties, which means you can't control what DNA is being transported. Minimizing the chances of escape seems only prudent.
