Leeks

That looks delicious. Do you have a recipe?

It sounds more like you want a cross posting feature. There is no reliable programmatic way to determine both threads are about the new show, and anything that’s not reliable and programmatic is just ripe for abuse.

A cross posting feature would be nice, but for something like “the new episode just dropped” without some serious coordination between the communities, you would still end up with a lot of threads.