Want to "freeze" some coins with some new private key? Just create new account with this key, trasfer coins to it, and then use this key only when you need to spend this coins.
The problem is that the "lucky gold strike" loophole for somebody else to hit this new account when miskeying their own password exists just like it exists for the old one. Psychologically to the public this is always going to be perceived as a flaw because they don't understand how unlikely it is. You haven't increased security one iota, you have only created a different winning lottery number.
Publically announcing to the world not to accept withdrawals from an account closes this loophole. That will make a huge psychological difference to the public. And I am telling you, for NXT to succeed with the public, irrational psychological issues are going to have to be addressed.
You still need a pass at some point to make an announcement like "I want to spend this money again" right ? you would still need to enter this pass into the network right ? It is essentially the same thing as current implementation.
No. If it is a dual colored coin scheme, attempts to unlock the account for withdrawals are publically seen on the blockchain and can be monitored and throw up warnings that an account is under attack. If somebody hits the powerball jackpot and gets into an account through a miskey of another password, that is a one-time private event that is all over in under a minute and nobody even realizes it has happened until the next time they open their account or check it on the block chain.
I understand the math on how unlikely it is that a miskeyed password could open the fattest wallet by accident. This isn't about math. It's about public psychology. Saying as a programmer it isn't necessary ignores the popularity of Powerball in the public mind and the psychology bias it introduces against brain wallets.
If you use a random generator, the chance of someone mis-types and get your pass is zero. Because the pass will use a lot of special characters and not-well-placed keys. Pass like that cannot be accidentally typed. No humanly possible guess is a random. So no mis-type is not possible even in a billion year.
I only worried about hacking. But just educated myself with some current articles on password picking, I can say that it is already extremely time- consuming and impossible at current state of art to pick a 10 character pass if they are truly random.
Now key logger is another topic and definitely a risk. As long as you connect to Internet, there is a risk.