Another thing to keep in mind, is that if the size of Lemmy.world is already causing so much problems, imagine what would happen with threads...

Technical problems aside, I am against big instances, a single entity holding so much power is a problem no matter who that entity is. I would suggest creating a policy against that, but it's hard to figure out concrete limits against such instances, maybe no instance should hold more than 50% of MAU?

Last but not least, as others have said, threads is known for their poor moderation. Cutting off trolls early is important in creating a healthy platform, the more space and attention you give them, the worse they get. Threads is not ready to deal with that, nor does it have the incentive to do so.