Sony US patent Number 20140204265 discloses the design for two new Full Frame prime lenses. The 20mm f/2.8 and 28mm f/2.8. These primes are designed to be very compact and high speed autofocusing lenses. As Sony writes these lenses are suited for both still and video shooting and have fast inner focusing.
The 20mm could be the updated version of the current SEL-20F28 while the 28mm lens would a complete new entry. According to the patent both lenses will cover the APS-C sensor area only (no FF).