If Pokémon was more like digimon, then it definitely would have a Light-type. Since it isn't, I don't see it happening, specially after Reshiram which was THE candidate for such thing (because of the whole Black and White thing with Zekrom and the concept of Yin Yang), but they didn't do it. Also, Togekiss would indeed be a good example of a Pokémon being Light-type, due to its angelic appearance, as it has been mentioned... Another one would be the Blissey line...
Another thing is, as complicated as triple types would be, it would make sense for some pokémon to be triple-typed. Mainly pokémon like Charizard, the Bug/Poison bugs that fly, Vibrava & Flygon, Hydreigon, Reshiram and Zekrom, etc. Sure, Levitate remedies that for some (Flygon, Hydreigon), but Reshiram and Zekrom clearly fly, yet they still have to get an Earthquake in the face because they don't have levitate...
Another thing is, as complicated as triple types would be, it would make sense for some pokémon to be triple-typed. Mainly pokémon like Charizard, the Bug/Poison bugs that fly, Vibrava & Flygon, Hydreigon, Reshiram and Zekrom, etc. Sure, Levitate remedies that for some (Flygon, Hydreigon), but Reshiram and Zekrom clearly fly, yet they still have to get an Earthquake in the face because they don't have levitate...