sounds like cutting down a tree when it gets too big rather than preventing it growing like that...
i'm quite sure companies like google, apple, facebook, etc. are creative enough to find a way to get around this restriction which will just ensure a false sense of security.
i get the whole monopoly and fair competition issues, but haven't there been rules and regulations for those for quite a while?
apart from that: how realistic is this scenario to get actual laws enforing it when those same companies are pretty much funding the government?