I'm not sure what I think of the idea but it sounds like it could be plausible.
I first thourght of this when I hered that some people were considering "Sound" as a new type, I didn't like that because I thought about what would happen to Bug Buzz.
But I realise their are a lot of moves that could fit into two different types; for example the elemental punches. Thunderpunch could be Electric/Fighting?
I realise this could make things very very complicated but Pokemon is already complicated, it's not beyond their capabilities.