Sigma CEO Yamaki said in a Dpreview interview:
We need to develop more super telephoto zoom lenses for mirrorless in the future. We already have the 100-400mm F5-6.3 DG DN OS | Contemporary. There are relatively few lenses of this type in the market for mirrorless, so we’d like to introduce such lenses soon.
From a business perspective, Canon EF mount and Sony E-Mount. In terms of revenue and volume. However, the sales of DSLR lenses are declining sharply in many countries, because not many new DSLRs are being released. So, I think mirrorless camera mounts will be more and more important in the near future.