Apple filed a new patent that discusses using an OLED backlighting unit (BLU) for an LCD display. According to the patent filing, an OLED BLU unit may be thinner than a LED BLU and also have an improved light uniformity without using light guides. The BLU may act like a 'one large white pixel', but Apple also discusses the option that it may have several controllable 'areas' which will receive grayscale image information which may be used to modulate the light brightness (like local-dimming in full-array LED panels). Finally Apple says that the BLU will include one or more 'OLED units' bonded between two glass pieces. We're not entirely sure what they mean.
Using an OLED BLU for an LCD display has been discussed before, although it seems that it will not be a very efficient design - if you have a white OLED, why not use color-filters and not an LCD at all? This is the architecture that LG Display proposes for its upcoming OLED TVs.