The counter argument is that bitcoin devs/investors might not WANT the new feature that makes Bitcoin2 special, or regulators and lawmakers may exert a lot of pressure to not include it.
For example, look at zerocoin. Supposedly they are going to launch an alt-coin that will offer real anonymity. The bitcoin community seems to be a house divided as to whether that is desirable or not.
The Bitcoin devs wouldn't need to be involved in the zerocoin fork which preserves the Bitcoin blockchain, although it would help (as described on the OP). In your case, there would be three coins: Bitcoin, Zerocoin, and BZcoin (zerocoin technology with bitcoin blockchain). Assume you're a Bitcoin user who cares a lot about anonymity. All your current holdings are in bitcoins, but you know you want to switch to either Zerocoin or BZcoin. There's a built-in advantage for you to go with BZCoin if you already have a decent number of bitcoins, because you automatically have bzcoins for "free."
Btw, I know the Zerocoin blockchain is totally different than the Bitcoin blockchain, but I'd be surprised if there weren't some way to allow people with Bitcoin private keys to claim bzcoins.
No i think this is wrong. The coin that surpasses bitcoin, if a coin surpasses bitcoin, will be one that discovers a better proof scheme than proof of work.
The point is that a clone of this hypothetical coin with a better proof of work which preserved the blockchain would outcompete a version that didn't preserve the Bitcoin blockchain.
I think we can use another way to include Bitcoin block chain in Bitcoin3 with lower complexity.
The new Bitcoin3 can have a protocol compatible with Bitcoin network and accept to exchange your Bitcoin into Bitcoin3 with 1:1 exchange rate.
The protocol defined a plain text and valid Bitcoin address like 1YouCanGetBitcoin3BySendBitcoinHere to ensure that no one owns its private key.
And if bitcoin owner send bitcoin to this black hole address, Bitcoin3 protocol will create new Bitcoin3 coin and bind to the owner's Bitcoin3 address.
Then the new Bitcoin3 coin can run a completely new block chain or blockcahin-like structure and any other crypt algorithms.
Interesting idea!