Elemental fusions: These were more jutsu you could achieve through becoming chunin and having a certain amount of jutsu from another elemental tree. Like with the s rank scrolls this requires a balancing act to implement as it adds a lot of new things that could end up being overpowered if you used in a way thats unexpected from the developers
Source for elemental fusions: https://www.tapatalk.com/groups/goa_naruto/viewtopic.php?t=201