Frames could be just e-ink without any electronics, just with connector to some docking/loading station for choosing/loading image to display. Then you can make them really thin and sell them without any frames so customer could frame itself.
The only problem I see right now is really low contrast of current e-ink. When I look at photos displayed by Kindle they look dull and flat.
You will need electronic and driver supporting high resolutions for dithering if you want good greyscale reproduction. E-ink has quite high native resolution, the only problem is to control this as I remember well. But in case of frame it could refresh several seconds, so it won't be a problem.
I have no idea how much i.e. 10" e-ink panel will cost, but if price isn't high, such dumb frame with just connector should cost much more than e-ink itself. Even with simple card reader and system it shouldn't cost much more.
Anyway, I like this idea, but I'm not sure if it's possible right now because of low contrast of current e-ink.