This sounds like a good idea. Is the plan to put the blockchain up as a torrent to be shared between nodes to speed up the tx download/upload process?

stores are not allowed to sell the same goods for a cash discount vs credit card

What is the impetus for every day use?

That would make the suppliers and staff really happy making business with you.

Adoption drives the price down, stupid. Don't you know merchants convert funny money into real fiat immediately? They are not stupid.

1. You are missing something.  The nature of the protocol ensures no one can spend more than the balance that an address contains. If you could overdraw an address bitcoin would be worthless. (Using the concept of balances at addresses as shorthand.). If you are talking about something you didn't say, the total balances at any address for which you control the private keys, your client can enforce whatever rule you want, but the protocol does not.

2. By default Bitcoin Core doesn't reuse addresses and consequently private keys either.  Hence change addresses, new addresses for each transaction etc. Reusing addresses can cause security issues such as the android PRNG issue for reused addresses so it is already not recommended.  If that is the concern, a rule disallowing address reuse might be considered (I don't think it is a good idea either, it too could be enforced client side).

Anyway, if your computer is compromised you are screwed either way.  The difference in security between having a second layer at that point is de minimis.

As an aside, the odds of this being adopted by everyone are infitesimal when you can accomplish the same thing (or more) with good security on the client side. It is like adding email at the tcp/ip layer vs on top of it with SMTP.  You want the lower layers to be simple so they are easier to debug and here it is even more important since if you lose an email it can be resent, vs potentially billions of dollars at stake with bitcoin. 

You can always implement what you suggest and then see how many people will adopt it.

True. 

Likewise, if I understand what you are suggesting, I do not believe this adds anything in terms of security that could not be done at the application level vs the protocol level.  In either case (creating/changing your rules with your private key etc) vs bitcoin as it is now, if someone has your private key, you are screwed because they'll just change your rules and then transfer your coins.  A root cause of insecurity is protecting your private keys and adding these rules doesn't help with that. 

Clearly, you believe that the blockchain contains a collection of all generated Bitcoin addresses, which is simply not the case. That is why your proposed idea will not work at the protocol level.

You seem to be missing the point. Once your wallet.dat file is compromised, then your attacker can just load it in one of the many existing Bitcoin clients. And you can't hardcode those suggested "features" into the wallet.dat file itself without making it incompatible with other Bitcoin clients. Hackers can hack both wallet.dat files and Bitcoin clients. Those are 2 different things.

here we go! new theme song?

https://www.youtube.com/watch?v=ETfiUYij5UE