love the idea, but logins are not dead, you just piggy backed on device/passcode combination instead of email/password combination.
PS: I have always wondered why PINS from debit card are 4 digits, and some random consumer product will ask you for a crazy complex password with at least 8 characters.
As the story goes, when John Shepherd-Barron[1] was working on the original ATM system, he originally planned 6 digits, but reduced it to 4 because his wife wasn't able to consistently recall a 6 digit random number.
If true (and it sounds at least plausible), then the sheer number of legacy devices that expect a 4 digit PIN (including hardware crypto modules, which cost an absolute fortune to design and verify)
And, of course, a numeric keypad is much smaller and easier to design around than a full qwerty (and probably internationalises better as well)
The Cambridge Uni security group have a nice paper on PIN security in more detail, if you're interested[2].
I think 4 digit pins are so prevalent because they're easy to remember. As they get longer and harder to remember, people are more likely to write them down etc.
PS: I have always wondered why PINS from debit card are 4 digits, and some random consumer product will ask you for a crazy complex password with at least 8 characters.