I know this is far fetched, but the guy has some pretty cool ideas, even if they would be super hard to code.
My favorites are below:
The phantoms being a counter to elytra and current sleeping exploits is probably the coolest.
Description:
https://www.youtube.com/watch?v=30BmmdCnc3A

Next would be be drowned, actually drowning you, rather than just being an underwater version of zombies.
After that, making nautiuis shells spawn only in underwater caves, giving underwater caves a purpose that makes you want to explore them.
And finally, making tridents obtainable through ocean monuments.
Descriptions:
https://www.youtube.com/watch?v=KNwi8gPengY

There might be more, but I can't remember right now. Might update this later.
Thanks for your consideration.

Fantastic ideas! Will look into them shortly and update the issue.