I think one of the key things that will prevent the capture of the Fediverse by corporations is never ever allowing whitelists for instance defederation and blocking to happen.

If that ever does happen, it becomes trivially easy to break the decentralized network up into a few centralized silos that are all disconnected from the rest of the network completely, whereas, the way it stands now, you have to explicitly block anyone you don't want to be connected to, so it's a great way to deal with bad actors and nasty instances, but makes it extremely hard to wall off your instance completely, because if you block another instance it's trivially easy for the people that are unhappy with that to find or create a small new instance that flies under the radar and allows them to see the content on both the instance they left and the incense it blocked. It also makes it incredibly hard to capture people on your instance because they can always create a small instance and use that instance to see the content on the instance they left.

I think also limiting block list size for instances (but not users!) Could be a really good way of doing this too because then any instance I want to block a ton of other instances is going to have to fork lemmy to lift that band and then everyone will know they did that and know to get off it.