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Hold on a minute, let's go back to yesterday! Fatedquest, your original conclusions in all three scenarios were correct. With all due respect, binary vision is not correct about the effect of focal length on "compression". In the example linked to on Photozone, the position of the camera was moved in order to keep the size of the lamp post the same with all focal lengths. The changes in apparent relationships (compression, etc.) in the pictures is due ONLY to the change in shooting position. The focal length of a lens can only affect the framing and magnification (which are the same thing, for a given sensor size) of the image; it cannot change the size or position relationships among objects viewed from a given position. The only thing that can do that is changing viewing (shooting) position.
So for the conditions described in your #3 -- same shooting position and focus distance, different focal length to produce the same framing with different size sensors, same f-number and shutter speed -- your original conclusions are spot on: field of view, perspective, and exposure will be the same, but depth of field will be shallower for the longer full frame. The reason the the DoF is less for the full frame is not because of the size of the sensor itself, but rather the greater magnification of the longer lens needed to produce the same framing.
Disregarding image quality, noise, etc., and disregarding depth of field, then there is no reason you cannot frame the same picture in all other respects using anything from a compact point and shoot to an 8 x 10 view camera (and everything in between), assuming the availability of lenses in the appropriate focal lengths. As you correctly note, your shooting position determines the size and position relationships among the objects in the scene, while you would use focal length to frame the scene the same fore each recording medium format. Exposure would be the same in all cases. You would have difficulty producing the same depth of field in all cases, because the only variable you would have at your disposal would be the aperture of the various lenses, and they aren't likely to all have the range of f-numbers needed to produce the same DoF with their respective focal lengths. But that and image quality aside, you could produce the same pictures.