Wikipedia reports how guacol is the chemical compound used as reagent, interestingly is perceived by locusts as a swarm pheromone.
Vanilline is easy to produce, probably derived from aminoacid metabolism.
Regarding the "real vanilline" that's an elite product, it is sold mainly to restaurants and for end consumers that want to use the real vanille pod.
Expecting synbio vanilline to put at risk farmers is quite a hasty assumption, did petrochemical synthesis of vanilline do the same to farmers? they're still there.
Cool thing about vanille plant: it's an orchid, and it grows as a vine.
It spread much farther that it's geographical origin and because butterflies are inefficient or not present in alien environments it has to be hand pollinated. Plus not all flowers will produce pods.
Taking into consideration space needed (in subtropical areas: bye bye forest) and the agricultural practices in use, like fertilization, pest control and soil "improvement" that's quite a footprint for the vanille pod industry.
Best,
Fede