Thanks for the replies. In Stellarium the sensor view does give you a fov box on the sky, and you can set your own lens focal length. But the sides of the box are straight, regardless of the projection used for the sky map. Here's an example with an 8mm lens on a DX sensor:
In reality, the sides of the fov of a real lens would appear curved, even strongly curved for very wide lenses, and the curvature has to depend on the projection used for the sky. So Stellarium can't be accurately drawing the fov, especially for wide lenses. That makes it harder to plan shoots precisely.
Another problem is that the curvature of the sides of the fov has to depend on the lens projection: the sides of the fov of an 8mm rectilinear projection lens will have different curvature than the sides of the fov of an 8mm fisheye (eg stereographic) projection. But you can't select the lens projection in Stellarium.
There is also a ocular field of view, which I beleive is what you would see through an eye piece. for the camera, lens, and eye piece. i guess if you would create your own eye piece of a magnification of 1, that would give you a curved field of view.
Ocular view only gives a circular fov outline as far as I can tell, so it's not useful for planning SLR lens shots.
I may put in a request to Stellarium for better treatment of sensor fov's. Or write my own code!