No.
If they wanted a Light type, the previopus gen was 'the time' to do it with the legendarys of Reshiram and Zekrom possibly fitting it. But we didn't due to a number of things (a need to change game mechanics (e.g. Hidden Power which is based on the IV system)), and the bigger fact of the type system as is
is already pretty balanced which is unlike the case in RBY. This is not a game that is going to parallel GSC in any way (if that was the case, then why did B2W2 exist when there was no such sequels in gen 1? Answer: they are separate games!). The only reason they made new types was to nerf Psychic types which were way unbalanced in 1st gen. Now there's no such need.
Then consider how they'd handle previous Pokemon that could qualify as a new type. Change the types and contradict canon set up for over a decade? It was okay with GSC as hardly anything got changed, but now with 649 Pokemon in five gens? That's too much, especially with the type system established for over a decade now as-is.
As such I really don't see this happening, but I did see this sort of discussion happening as it does every gen at least. =p Oh well.
Just to clarify, the light type would be the polar opposite of the dark type. Dark type Pokemon are associated with darkness and evil so light type Pokemon would be associated with purity and holiness.
Arguably the counterparts are Psychic and Fighting! Dark is more to do with underhand/dirty tactics in Pokemon (see moves like Faint Attack, Bite, Foul Play, etc) which can overcome Psychic types. Fighting can be thought of as 'pure' clean fighting, which can overcome said tactics. Or so that's one way to view it. Thing is there is no need for a 'counterpart' to the Dark type, as it already exists in a way.
And again, what happens with Pokemon like the Togepi line? You could call them Light type based on Pokedex entries, etc, but then what happens to Togekiss, the Normal/Flying type? Something's got to change there. Then apply that to a good fraction of the existing 649 Pokemon. Yeah...