They don't even need an effect for the (spoiler) syndrome.
>!Masefield syndrome!<doesn't need any kind of in-game effect, it's coded right into every player the moment they see the>! World Tree!<.
Guess what my boyfriend did the very first time we played Subnautica 2? That's right, he went straight toward the massive eldritch thing on the horizon. He didn't even want to scan it, he just wanted to see if he could reach it. He was (eventually) reprinted.
Each and every one of us already has Masefield syndrome. Will there be added effects to show the decomposition of the players' mental state as they succumb to the beta Proteavirus strain and heavy metal poisoning? Probably. But that impulse is already part of us.
After all, how many people swam straight toward the Aurora in the first game? I'd be willing to bet most of us did.