I think an Apple Tesla partnership is more likely than Apple directly competing with or buying Tesla. Sometime last year, Musk spent some time at Apple, Tesla has the patents and Apple seems like the right company to license the technology. They're also a great partner for the gigafactory because they can get laptop batteries for cheap + batteries for their electric vehicle.

Also, if you're Apple and you're interested in getting into the car game, why build a minivan? A minivan is hard to design beautifully and doesn't have mass-market appeal unless you're not trying to compete with Tesla. If you're truly interested in disrupting the automobile industry, you're creating a premium luxury sedan - the 3 series of electric cars.