According to a recent interview with Kazuto Yamaki, CEO of Sigma. Sigma is planing to make a 50mm f/1.4 lens for Sony full frame mirrorless cameras. This lens will compete the current DxOMark king Sony Zeiss FE 55mm f/1.8 lens.
From Kazuto Yamaki:
A lens like Sony’s Zeiss 55mm F1.8 for the FE mount is optically superb but quite small and light. If you were to design ‘Art’ lenses for that system, would you try to strike a different balance between quality and size, and try to make the lenses smaller?
Yes – that’s also one of the segments we’re interested in. Another motivation for us to make new lenses is to differentiate between other manufacturers. Sony already has a 55mm F1.8 which is nicely sized and reasonably priced, so why make another? But F1.4 compared to F1.8 is a huge difference, so we’d either make a F1.4, or something different.
via: dpreview
Read More: Sigma Rumors

Please make a wide angle. We have enough 50mm lenses. If you could make the great 10-20mm wide angle zoom lens for FE mount it would be great.
Is there more than this quote to substantiate your claim? I don’t see anything here that says Sigma “will” make FE mount lenses. They might, and there might be a 50mm. Personally if they were to adapt an ART prime I think they new 24mm would be the most likely candidate. That’s a big hole in the Sony system.