Hi Tommy, and welcome to the world of Sigma cameras. I'm glad to see you added some equipment to your gear list here, and I hope to see some of your photos posted in your gallery too.
I see you're a Pentax shooter, as well as a Fuji shooter. I too have other brands of cameras. Still, I love the quality of images from the Sigma cameras best. In the future though, I plan to get a Fuji X-H2. Why? Because it looks to be so versatile, and the image quality should be at least close to what I can get from a similar sized Foveon sensor. Also, even though the performance will surely be lacking, when compared to my full-frame Nikon D810, the Fuji should be able to do high-ISO photography much better than a Sigma camera with a Foveon sensor in it, like a Merrill or a Quattro. Add to that the amazing IBIS, excellent articulating tilt screen, and the ability to shoot 8K video in a camera that's priced under $2,000, and to me it's a no-brainer. I mean I'm already a multi-system photographer, right? What's another body and two or three more lenses? It'll give me the ability to do stuff that I just can't do right now.
As far as the future of Sigma cameras goes, I believe we will see Foveon sensors in new Sigma cameras in the future, though it appears that they won't be called Foveon anymore. They won't dominate Sigma's camera offerings either, since Sigma now makes cameras with CFA sensors now too (just like every other camera company). Foveon was never mainstream, and it appears it never will be, but I think it will make sense for Sigma to continue making them in order to differentiate Sigma from other L mount camera companies, and to help differentiate L mount from other mounts (like Nikon's Z mount, Canon's R mount, and Sony's E mount). In fact, I think Panasonic and Leica would be smart to get involved with Foveon sensor development, if Sigma will allow that, and help fund future three-layer sensors, because of how it will help L mount succeed as a mount of variety . . . not just of lenses, but of cameras and technologies too.
Foveon vs CFA is nothing like Betamax vs VHS. Betamax had a huge, industry leader behind it, but Sony made the mistake Apple made many years ago, and refused to make their format an industry standard by licensung the technology cheaply (or for free) to competitors. Instead the bulk of the industry made VHS compatible products, which brought down prices of VHS players, which in turn increased the demand for VHS tapes, making VHS the dominant player. Foveon never had a significant place in the camera market, and was never a big player. It appears it never will . . . unless some new design gives it an edge in the future.