It's a little late for unique identities. Try telling the 50 'joeblow' ID's on 50 sites that 49 of them have to give up their ID.
The '1 ISP' concept you mention is for tournaments only. There are too many reasons to list here why people use more than 1, and they can be quite legitimate reasons. There are a lot of players who never play in MTT's, not to mention cases, like my own, where there are 2 of us here who play but cannot from one machine. When my SO wants to play, she goes to a neighbor's house to use their computer. Since we have 2 accounts at the same address, we do have to play in different games.
We could all come up with tons of ideas. Some might work, some not.
What I think the online poker industry needs is a central, international regulating commission. Besides establishing 'safe and fair' mandates that would require poker sites
to meet certain standards in order to receive their 'certification', they could also establish an international clearing house that would maintain a database much like credit reporting agencies. It would include a list of those banned from a site for cheating in any form. It would be similar to the clearing agency used by banks to check a new customer's application for an account. If you are on the 'bad customer' list, you do not get an account.
As it is now, any player banned from a site simply goes to one of the myriad of other sites to ply their cheating trade.
The industry itself has to make the first move to assure customers they operate fairly. Their lack of interest in such a move does give us cause to ponder why they have not done so yet. When these companies make millions of dollars EVERY DAY in rakes and players still deposit BILLIONS of dollars into their sites, why would they want to fix what they do not think is broken?
If your customers were depositing billions into YOUR account, willingly, would you want to rock the boat or question the result?