I'm surprised this hasn't yet arisen in this forum for discussion -- as it variously has here:
https://www.dpreview.com/forums/1027 -- that a new firmware update for these Foveon cameras permits saving in the more universal DNG format as well as the limited Sigma-proprietary X3f format. Options for processing by more RAW-converting apps is deemed one of the primary advantages. (The new firmware also introduces a new HDR-type option for these cameras, labeled SFD.) Interesting move by Sigma.