Adding T7-T9 manufactories doesn't mean they will use seeds to produce them. I am almost sure that the trader will produce something else to produce this new type of goods.
I didn't bother reading the current event that carefully but from a story line perspective it would make some sense if we started to open up a trade route to Unur. There is a good chance the trader will collect some type of new goods from there that we can use to make new goods with.
not the first time they have used quests to introduce future stuff. Of course this is a complete guess.