This is the example I hear brought up all the time about how ISPs could rearrange internet access through throttling. I understand they could do that. But how likely do you think that outcome is?
I'm not sure it'd look exactly like this; I think they'll be more subtle about it. They know that with the bru-ha-ha created by the FCC's decision, they'll need to act slowly. There is also 0 doubt that lawsuits will be filed against the FCC the second the vote happens, and they have to be at least a little careful that they don't create pressure in Congress to do something. They also don't want this to be a campaign issue in the midterms.
We might see some relatively invisible things, throttling BitTorrent for example. And possibly taking steps to harm Tor, or any other protocol, service, or site that they can pass off as shady. But even then, they run a different kind of risk: if they start being too aggressive about policing the Internet, they have to start worrying about being blamed for the stuff they don't cover.
My guess is that rather than outright bundling sites together and making them inaccessible, they'll couch it in opposite terms: buy this plan to get faster service on these sites. They can deny that they're slowing down traffic, even when they do, while then saying they're offering people a "choice." I also think most of the pressure and cost will be for sites and businesses that depend on the internet, since it's harder to get people riled up about that. "So Google has to pay extra because they use so much? That seems fair." And Google will do it, because what's the alternative? But once they do, and consumers don't see a difference, suddenly it's much harder to criticize.