Currently, the site's policy is that if a post announcing these types of changes gets 7,000 comments, the changes are put to a vote.
If 30 percent of Facebook users vote, then the results are binding, otherwise, Facebook can do as it pleases. This system hasn't worked out very well in practice and is, in fact, one of the things Facebook wants to change.
But, as you can imagine, getting 7,000 comments on this issue wasn't hard, the site has one billion active users. So now the changes have to be put to a vote.
It's all very meta, users get to vote on whether they are allowed to vote. While critics of the move are optimistic about the turnout, the fact is 300 million people are not going to vote on this, presidential elections don't get anywhere near those numbers.
So the whole endeavor is rather pointless, still Facebook has to go through with it. A vote will be put up soon and users will have a week to make their choice. In all likelihood, the results, i.e. the low number of people who vote, will legitimize the changes, but we'll have to wait and see.