The way I see it, the system currently works pretty well. Account sharing isn't totally free for the user.... you only can have a certain number of simultaneous streams, and you will have extra profiles on your account.
If people can afford their own account without sharing, they will do it. If they are sharing an account, it means they are sacrificing some functionality to save money.
I have a group of friends who share a Netflix login and split the bill.
It took them several months to realize there was a simultaneous streaming limitation because it was so rare for 3 of them to try to watch at the same time.
When they hit it, the third person just watches on their shared Hulu or shared HBO account anyway.
If people can afford their own account without sharing, they will do it. If they are sharing an account, it means they are sacrificing some functionality to save money.