In my opinion, it'll probably never happen. It's already impossible to filter plaintext spam emails via heuristics with complete accuracy, and the 'spam folder' in every email inbox is a concession to that so that customers don't lose important mails that're occasionally mislabelled. Blacklisting packet content like BitTorrent packets is already impossible because of encrypted protocols. If ISPs take a heavy-handed approach to filtering content at the file, protocol or packet level it'll just push P2P networks and sites down the same route.
The only reliable alternative is whitelisting, and if an ISP wants to whitelist every bit of 'legitimate' content on the internet forever more, they're welcome to try.