The ability to choose cameras from a pulldown on the vfb, and have the vfb/ipr lock to the selected camera. Default "active." I believe max has the "lock" to camera which I've used before however I end up losing track of it because its somewhat abstract and I believe it's in the render setting. A pulldown of listed cams on the VFB would be perfect.
The rendering camera could be simply set in the viewport in the View - > Use As Render View option enabled.
I think this ( the current one) is the best option as you can directly set the render camera in viewport and don't have to remember what you'd set up in the VFB. In my opinion adding this feature would make for a lot of confusion during render time, and its just more prone to errors than the current setup.