A 3D movie consists of two pictures, one per eye. Two 4K displays are redundant for a current 3D bluray, which picture is 1080, but image could be upscaled and sent to each display. in this case there should be no black bars.
Probably you want to say that in this case the two pictures wouldn't be correctly aligned for the eyes, since the Pimax is designed to provide a 200° field of view. So I ask you a question: when you play a game, what do you see in each display? Is the picture deformed to cover such a wide field?
As an alternative, a movie - which picture represents a narrower fov - would take a subset of the available screen space, and here's the bars you mentioned.
It's a pity that none of the exiisting viewers allows watching movies from Blu-ray discs, directly or through a player . Such an option would provide a cheaper and more immersive alternative to 3D TV sets that are still expensive.