Sorry, must have missed some posts (there sure are a lot of them!).
However I feel that my first point hasn't really been discussed much - i.e. an option where the camera is like the current unlocked camera except for when your champ is moving towards the edge of the screen, then it follows your champ to keep them in the central area of the screen. An option along these lines would avoid having moving targets when you move yourself, and thus lower the potential for mistakes in tense moments of the match. In the OP you quoted a discussion on focusing the camera on the center of mass of champs, although I think that option would cause some wiggling of the camera and sometimes may change on the player during intense moments.
Anyway, I thought I'd put my 2 cents in. Rioters are pretty good at what they do so I'm sure you'll come up with something, just trying to give you some ideas. Feel free to ignore if you don't think the idea has any merit.
Consider walking up to harass a champion:
* With locked camera you will see the same amount in the direction you're walking (and are interested in!)
* With your scheme you camera would be static and you would walk up to harass, but not see more of the interesting area (around your target)
So actually, I think you might want something similar, but which moves the camera in the opposite way so that it moves the camera in the direction you're walking. This is more complicated than what you propose though, it would require a lot of logic to make sure it doesn't feel jerky and bad as you're micro-ing in lane.