Three new patents (see: 1,2) have been issued from Sigma for a 300mm F2.8 lens, a 250mm F2 lens, and 200mm F1.8 lens. These appear to be for the Sony E mount, at least initially.
We don’t have any other information at this time, and it’s not uncommon for patents to be filed for lenses that never get made. But hopefully at least some of these lenses get made. As a bonus, we hope that Sigma makes them significantly cheaper than first-party offerings and keeps the weight and size down as much as possible.