I think it would be really cool if this didn't happen so players on multiplayer could decide to temporarily private their base by removing the key.

I like the idea! I could definitely shatter the portal blocks on both sides. (Unlike dungeons.)

Doing so makes it possible to trap someone in there. I need to think if there are any other exploits.

Maybe you could make it so the main door can't do it but other ones do so players can't get trapped?

I do hope for this feature because it'd be a really beneficial change, with another reason being that the current system can cause issues if players want to completely remove their portal, but other players are still able to travel to their base.

And on a somewhat related note, are there plans on letting players customize the hubs? Maybe the prebuilt keyholes in the hubs could be made craftable and coded, I don't know. It would be a really cool feature though, but I understand if you haven't added it yet due to time constraints.

I'm considering it, but I don't know how to code it safely. The teleporter hubs are in the dungeon dimension, so the block protection applies the same as all the dungeons. Fortunately, I do save the dungeon type for each chunk, so I could check that. But checking that fro every block break and every block place would be slow.

Depending on how public your world is you could turn block protection off in the server config, edit the teleporter hub in survival mode, then turn it back on. The current aesthetics of the hub don't consider game balance if you do that, but I don't think I built with diamond blocks or anything.

I just implemented your suggestion! I also made it so that the 'oak' door is an exception to this rule, to prevent players from getting trapped.

Implemented in the latest release! Download v172 from CurseForge.