We’ve seen that there can be beings capable of wielding multiple elements, a la the Makuta, as well as Toa that have been fused a la Prototype.
We’ve also seen that a Toa of Light can become a Toa of Shadow, and that you don’t need a mask of Light to give light powers (although I don’t know how many cases other than Takanuva we’ve seen). (Creating a Toa of Light?)
So both have been demonstrated, unlike other elemental powers, to be able to be gained and lost.
Could there theoretically be some way for a single toa to learn/gain/awaken these two elemental powers?