I would possibly look for a two-disc Cars to be announced around the time of its Blu-Ray issue in June.
Other than that, we need to wait and see what the features are for that version. If there's nothing amazingly new, then look for a double dip on DVD and Blu-Ray either for Christmas or sometime next year. If it DOES come stacked with new bonuses (and an "immersive Lasseter commentary" has been talked about) then I'd say we could be stuck with our current DVD.
So, I guess Pixar hasn't announced anything about a 2-disc/extra features Cars set yet, only Blu-Ray?