Gizmodo Japan published an interview with Sigma's CEO Kazuto Yamaki where he confirmed that the company is working on new small L-mount mirrorless full-frame lenses to fit the Sigma fp camera:
"The camera itself is good, but the rest is the lens. The world view cannot be established unless the number of compact lenses suitable for SIGMA fp is increased. Regarding that, various developments are in progress, and it may be recognized that there will eventually be something suitable for SIGMA fp. I want to develop the camera itself."
Source: Gizmodo (translated), via Digicame-info (translated)