additional effects are tricky, because it turns options into must haves and even with the "limited" options we have atm we are still faced with BIS(Best in slot) mentality. Additional effects would just increase it further, so what if you are i130, you don't have additional effect flash grants DoT damage you are gimp or so you have a i130 weapon but it's not the i130 that increase potency of your ninjutsu so you are just gimping yourself.

Basically it's just a trickery slope to add gear with additional effects because it just becomes another thing to balance. Maybe they will try it but honestly if they did I hope that maybe they just keep it tied to accessories since in all honestly, accessories are meant to be magically enhanced items that offer effects based on which you are wearing. So you could keep armor as is and just have accessories be a more diverse set of options that could have additional effects on them.