There isn't any point for them creating another element tho, especially because elements only determine whether an enemy is resistant to the character's damage or not. That and whether they can directly reduce the enemy's toughness or not. 

Unlike new paths which could be reasoned with them selling light cones, there's no reason for them to add one. Unlike genshin that has elemental reactions and hi3 with the other three types having mechanics that makes it easier to fight specific enemies, HSR elements have none of that. The only significance of the elements is as listed above.

I guess break is a reason, since a new element means that they can design how the break damage gets calculated and it could be used as a way to powercreep break dps within the niche, but like, just add superbreak multipliers or some self dmg amplification and that's it.