Thinking video mainly here... I think Sigma is in a great position compared other Japanese camera manufacturers, and that's because they don't have to protect some pro cinema camera line up like Sony, Canon and Panasonic needs to. These companies will always hamper their consumer cameras in some ways in order to not cannibalize the pro line up. Sigma has no such problem. If they can do it technically, they could create a consumer/prosumer cinema (hybrid) camera that rivals the highest end cinema cameras and not think twice about it, and possibly disrupt both the pro and consumer market segments. If they can, they should.
In my opinion they shouldn't concentrate on the resolution game, 8K, whatever. That's not important in vast majority of applications. And in those applications where you need 8K or 12K there's cameras that can do that now. The most important thing to concentrate still is the dynamic range and that's where Sigma's focus should be. I take higher dynamic range over higher resolution any day of the week. 4K is plenty, but the dynamic range of Sigma FP isn't. It's good, but it should be better.
Foveon sensor cinema camera would be nice to have (at least as a technology demo), but it's probably not going to happen any time soon, if ever. If need be they should use the sensor know-how they have in-house and develop their own high end CMOS sensor (again concentrating on dynamic range and color more than resolution).
But why am I saying they should do consumer/prosumer cinema camera and not a high end expensive pro cinema camera? Because as a market, it sucks. I greatly doubt anyone is going to get rich by selling pro cinema cameras because volumes are so low, not to mention the whole rental house game. Sigma already knows this from their cinema lenses. That market sucks too, but it was a no-brainer to enter since they had the lenses already. The money is in the consumer/prosumer market and that's why Sigma is in great position, because they don't have to worry about existing pro line up. They can create whatever they want as long as it's technically possible and doesn't get too expensive.
Oh, and the next camera needs to have OLPF. Need that for video.