The MHL and Wi-Fi Alliance websites published a list of upcoming products in 2015, and there are several new LG OLED TV models in there, in 55", 65" and 77" sizes. All the OLED TVs from LG in the past year has been curved, and LG did not release a flat OLED TV since the Gallery OLED TV in September 2013, but this may change soon.
The new models include the 65EG990V/65EG9900, 77EG990V/77EG9900, 65EF980V/65EF9800 - all likely to be 4K models - the EG9900 (in 65" and 77" models) will likely be the successors to the current 65" and 77" 4K curved models (the 65EC9700 and the 77EC9800) in the US (the EG990V is the equivalent model in the UK).
Speculations online say that the EF models will use flat panels (hence the F). This is a bit stretched but it indeed makes sense that if LG will release several new models, at least some of them will be flat as most consumers seem to actually prefer a flat model over a curved one.
There are also some 55" models (the 55EG960V/55EG9600, 55EF950V/55EF9500) and other 65" models (65EG960V/65EG9600 and 65EF950V/65EF9500). It may be that some of these will be Full-HD models, or lower-end 4K ones.
We'll probably know more early next month at CES 2015.
LG is very upbeat on curved TVs (mostly OLEDs) for a while now, as they believe they provide a superior image quality. LG also aims to release a bendable OLED TV next year. This may be appealing as it can be hung on the wall in its flat state and only curved when you want to use it.