That's what happens when your lens mount falls behind the times. /shrug Pentax users should be happy that there's a 3rd party lens maker interested in producing AF lenses at all.
Kinda like with Fuji, a potential Pentax user must look carefully at the Pentax lens selection and decide if they are suitable. They don't even really need more than a couple new APS-C lenses, but the paucity of new lenses for the 645-system hamstrings the product.
Anyhoo, I'm happy for Sigma that they have some neat, highly-regarded products, some which are different than anything else . A family company with a history of hit-and-miss lenses, it's nice to see them come into their own a bit. And Mr. Yamaki seems a bit chattier than the stereotypical Japanese CEO.