That's the best video I watched on the subject, seriously covers some hard pressing issues.
In theory Apple and other vendors are likely to release retina display x4 or even x8. In such events you will end up with a very big image, giving your mobile of computer a sense of reality, but at the same time giving us really slow internet. In such cases I can really see scalable vector graphics becoming on the scene as they could be scaled endlessly.
Retina display is very new, but looking at the way the mobile world evolves I would not be surprised if this change happened sooner than later.
I would love to see how retina display images work with adaptive images - http://adaptive-images.com/