It's something that is existing in Stencyl for example (i've nerver pushed a lot that software, but i suppose it works well) : you import your image at 4x, and the soft auto creates 2 others images (x2 and x1) to play the game at different sizes depending of the resolution of the mobile.
I know it would increase the ram, and the weight of the project, but it can be really usefull, depending of the project, to win a lot of fps on smaller devices (if i understand well how things work).
For example, i want my project to be an universal Appl app : i have to design eveything for the Ipad3, as recommanded by Ashley, but my Ipod4 has also to deal with the big images, and I think it's hard for him lol.
I suppose, but maybe i'm wrong, that I could win a lot of FPS if it was dealing with a smaller size of eveything.
By the way, maybe it's possible to separate the images folder too, and like that, just use the ram of the good image size.
Don't know if it's possible and if i'm clear. Maybe i'm asking too much, or maybe it's useless in fact haha.