There's no way to be sure yet. But it could be other types of hunters we haven't seen before. Maybe hunters from a far - off land with unique nen abilities.
The old and new story of Hunter x Hunter do match to a large extent. The lore and the power system are maintained throughout. The old story introduced us to the unique and complex power system of Nen, which is still very much a crucial part of the new story. Also, the overarching goal of exploring the mysterious world of Hunters and the secrets it holds is continuous. Even though new villains and challenges emerge in the new story, they fit within the framework established in the old parts.
Well, from 'hunter x hunter new story', we might see the return of our favorite characters like Gon and Killua. There could be new villains with even more devious plans. And the story might take us to new and unexplored parts of the 'Hunter x Hunter' universe, expanding on the lore and the power systems.
Well, it could be the new and unique plotlines that the fanfiction offers. Maybe it takes the original 'Hunter x Hunter' world and twists it in unexpected ways, introducing new characters or exploring the existing ones in greater depth.
Mostly yes. However, there are some minor differences. The new anime might have some updated animation quality which can enhance the visual storytelling. But in terms of the story itself, the important elements such as the various arcs - the Heaven's Arena arc, for example - are presented in a way that is faithful to the original story. The new anime also doesn't deviate much from the original in terms of character personalities.
The Hunter x Hunter manga is unfortunately not complete. The author has faced various issues that have led to intermittent breaks and an unresolved storyline.