They missed the boat, starting to charge now will just screw the install base now, and will discourage some cheapskates from purchasing the consoles - as it makes such a drastic difference in the first place. Since they didn't do it at the start, it doesn't make sense making it mandatory now, but they did provide an alternative - PSN+. Which isn't quite there in terms of benefits for value.
Disconnect and self destruct, one bullet a time.