The Polaroid SX-70 was the first SLR, instant film camera in the world. It was introduced in 1972, and I believe it was the first instant film that didn't need for the user to manually remove the film packet from the camera.
However, I don't believe that, unless you refer to "auxiliary" items that there were any "system" cameras, i.e. interchangeable lenses, etc.
Yeah... I was wondering about things like interchangeable lenses, filters, etc. Maybe multiple backs, like with medium-format cameras. I'm really just curious; there doesn't seem to be anything inherent in instant film technology that would make it impossible...
As far as I know, there are only instant backs that can be used with medium format systems.
It doesn't seem practical unless you use it with larger formats. Unless you want a camera with a built-in enlarger, you'd end up with tiny images no bigger than contact prints. Even 6x6 negatives are small images - smaller than most people want their prints, anyway.
The Polaroid 600SE isn't an SLR (it's an RF camera) but it has interchangeable lenses and backs. It was actually made by Mamiya and marketed by Polaroid under their name. It shoots Polaroid packfilm, Polaroid 4x5 film or regular 120 film depending on which back is attached.
I'd be guessing, but the mechanics of a Polaroid SLR would be awful to try and keep precise. The mirror, prism, etc., would be vastly oversized, and would probably sound like an old Graflex on steroids. An awful lot of mass just to get instant pictures.