Update: There's a short article in ZDNet Korea in which LG Display's CEO says that OLED TVs will be competitive with LCDs in 2014. LG Display will only mass produce them at that time. So it's not clear if LG is indeed planning the 5.5-Gen plant for OLED TVs or smaller displays.
Back in April, LG Display announced that it'll invest $225 million in 3 new Gen-4 OLED production lines, to go online in 2011. These will be used for small displays (for mobile phones). Now LG says that they also plan a new 5.5-Gen AMOLED plant in 2012, which will be used to make large OLED TV panels - apparently 50" ones.
LG didn't disclose how much money it will invest in this new plant. But Samsung's own 5.5-Gen 3-lines AMOLED plant (planned for 2012 as well) will cost $2.2 billion.