I think this is an excellent idea. Once a company grows beyond a certain market share/ market cap it gets split down the middle. Thus kind of happened in an ad-hoc way before, e.g. Bell. The only trouble is these mega companies have lots of clout and a strong self preservation instinct.
I would prefer if there was a way to do this with taxation or similar. So from a certain size on it would be more expensive to do business. I think this would be more gradual than a hard split.
