Was there ever a hypothesis about a planet called Biga?
If another planet in our solar system was to be named, I think that Biga wouldn't be the first name to come up, all of the known planets in our solar system are named after Roman deities and Biga is not a deity but rather a cart on which mostly Luna is depicted. I have never heard of this proposal and if the 'rules' are used for naming, it wouldn't be the first candidate.