okay first, I want to explain why I beleive 100 PERCENT that "light" type will neverevereverEVER exist.
It simply does not fit. Just imagine all the type names in your head, and add light in the midddle. It is a tottaly different kind of type that would belong in a differnently made game like yugio or sumpttin. The english names for the current types are definely more "western", like, mainly grass. If grass was called "life" instead of grass or ghost "spirit, it would sound more "eastern", like Yugio.
Now I think the IDEA of light type might be possible, and maybe called light in Japan; but I think the English (sorry, I dont really know about other languages, so I have no idea how "light" might come out in those languages" would be something like Fairy. Peersonally, I can see all the fairy egg group be a fairy type, but in no way can I see their english translation be Light. The only pokemon I can see as light is Xearneas. No others.
This is just my personal theory, and just to recap, I'm saying a type like "light" type, wouldnt be refering to the "Western" light; like acual light rays, but more "Eastern" like fairy-like, or good, or maybe even holy. I just could not see the English translation for it be Light; just like I wouldnt like dark type being called evil, which, IIRC is the literal translation of the Japanese dark type.