As I understand it there is some extra room around the 4:3 shot in the 35mm frame, so it's possible that when transferring off of the film (which they'll need to do anyway) that they could re-frame the shot to be 16 x 9 while still preserving the essence of the intended shot. That's how they did the widescreen Seinfeld that's airing in syndication.
Yes every show shot on film that is shown 4x3 has excess frame, but since they are framed 4x3 that extra frame could include anything. Cast in partial costume, people waiting for the next shot, equipment that wasn't moved (since it wouldn't appear in the 4x3 framing, to sets not fully dressed, ect. It can also be clear... But using material that was framed for 4x3 and using the full (if clear and available 16x9 is very distracting, as usually it lacks activity. There is no one way to do this that both mages to not screw with the framed design of the shot and show a balance of activity through the whole shot. No matter the technique used you do have to change and alter the shot.
Compare this to say the first handful of TOS restorations where they really did try and match each stupid star.
No matter the technique used you are altering. You can't even attempt a frame for frame match, which you can at least attempt (if you desired) with visual effects.