Rumor is that the next iPad mini will feature a Retina display. DigiTimes is reporting that the next iPad mini update will be mainly focused on increasing its screen resolution. They cite the source as Taiwan-based backlighting industry sources. These same sources also say that the next 9.7-inch iPad will use one LED bar instead of two for the backlighting.
If the iPad mini moves to a Retina display, it would likely feature a 2058 x 1536 screen, which would put it at 326ppi. It will likely see the application of Apple's current Retina display technology as that would be the cheapest for Apple to implement.
The sources also note that the 9.7-inch iPad will be switching to a single LED light bar for backlighting, with the overall effect of the change being a lighter device.