I don’t think he is the final villain. I guess it will be Someone around the would government, like Imu. Maybe Blackbeard is even following the same way to bring the government to fall. Blackbeard is a bad one, but he isn’t that big evil monster. Just compare him to the actions of a Kaido, or a DoFla. Right now he is on a partying island.
But yeah I can see this happenings around the porneglyphs coming. Maybe we can even get the three captains again at the last war against government, fighting together. :D