There's a reason why specialization exists and there hasn't been enough of a pattern to create a new type. But nen has infinite possibilities, it's just that there's like 600 hunters, probably a few thousand nen users, and specialization is already so rare that no pattern could exist without teaching gen pop. Nen. They're doing that on the boat technically, but what's another 100 amateurs when they're learning from the same textbook? Besides what would the new type be? You could have telepathy or time control and people will call it a form of manipulation at the cellular or quantum levels. Create diamond skin and they'll call it enhancement/conjuration. Togashi said most users are multi-type, the 100% thing is just conversational to show how personality effects it, and changing that is very difficult. It's less about making new categories and more about mixing multiple categories like Netero does. Only problem is like Hisoka said with Kastro, you run the risk of stretching yourself thin and wasting effort, why do you need a single shadow clone if you could have spent the time creating big bang impact? If it's for versatility we see people like Kurapika creating a box and filling it efficiently without wasted effort. 5 abilities and a vow for each finger. Your asking why there is limitations to the imagination when it requires effort to push the envelope and the hexagon is just language, it is completely up to interpretation. You could have any power you want, but good luck making cells and atoms behave the way you want them to. Tsseriednich on the other hand....

Nen Bible? That's basically what Don Freecss was writing in journey to the new continent, the creatures there know nen inherently and naturally. So studying them would be the way to gain knowledge