I mean, how exactly? They already have all 5 elements. I've suggested in the past it would be cool if you could have battle armor that changes their attributes or provides buffs to certain attributes but they aren't going to cause they can only implement things in CN version

Only thing for mains they should change would be to add both a male & female version so you can could pick either one. And the ability to unlock all secondary nature, so you aren't just stuck with only one option per main. (The way the interface is set up, it seems like that might be an eventually addition, if CN gets it.)

Other than that, adding more mains seems useless.

Unless they make some mains with Ice style, Magnet style etc I don't really see much of how you can change the mains. It would be cool, but it would take some money to design those mains and the abilities (and breakthroughs!) they would have

Crystal user

inb4 Yin-Yang main

I so agree with this idea, imagine a jinchuriki main *_*