1. If you require that hash(X) < Target, then one needs to iterate over parts of X in order to find suitable result thus proving certain amount of "work" has been done to find that solution and secure the transactions, making this a PoW coin.

2. There have been numerous discussions in this and litecointalk.org forum whether or not hash function should be memory hard and consequently deterring developments of asics. Although I'm personally on the anti ASIC side of the fence I believe there is more than one argument to consider here which is why I like your idea.

3. Allow me for a brief digression here: I'm not buying the argument that high hash rate makes network any more secure as for example I could develop a super machine that hashes at 100x the speed of all other miners in the network and by the logic of the hash rate=security network would be 100x more secure once I deploy it, however if I really did this I doubt anyone would consider the network (with one miner only) more secure.

4. So only a distributed network with lot's of users and miners makes the coin secure, assuming no such disruptive technology with potential 100x (or 1'000'000x) speed-up can be easily developed. (Which is a stretch I know)

5. ASICs clearly work against this principle as no one I know can tomorrow buy an ASIC device for mining bitcoin or other coins that would actually make a ROI. Just for the sake of example everyone I know can buy a PC with a GPU in any number of local stores tomorrow and mine some X coin with reasonable expectation of making a ROI. If I (and others) could buy an ASIC in a local store and use it to get my investment back I would sit on the ASIC side of the fence. ASIC developers over price their products making ASICs not friendly to miners.

6. Please note that mining pools also work against point #4 as due to economies of scale large pools are by definition: better funded thus more reliable and secure, better developed, probably offer better customer experience and offer lower variation when mining, so they attract more miners  creating a situation where top 5 pools by size control more or less most of the hash rate of a coin. So attacking say Litecoin would probably require taking out top 5 pools which is lot easier than developing "100x" machine from point #3.

7. So I think your idea would be perfect if it could solve both those problems. As someone on this thread correctly pointed our that adding a hash of some previous block to the header before hashing it would not do the trick as hashes of previous blocks could be precomputed I would go further to say that adding arbitrary memory requirement to the hash function would not work in the long term either as there is no real reason why ASIC developers could not bolt arbitrary amounts of memory (even DRAM or disk) to the ASIC as well still this makes development of such machines more difficult. I believe current term for such a coin is "ASIC resistant".

8. I propose (as you have) that the hash function only works efficiently when miner has access to the whole blockchain. For example sha256(block_chain_data(sha256(block_header))

9. I propose that hash function does not work efficiently in terms of forming pools (this may be impossible)

10. Thus miner variance should be made small by other mechanisms. Small block time does not work, but making the whole network act as a one giant p2p pool probably would. I was thinking something along the lines of allowing all miners to submit blocks with lower than network difficulty. Such blocks would not be considered as final as long as someone actually submits a block with lower than network difficulty. Then all miners would be paid proportionally to their contribution. This would open up problems with coinbase transaction which in an naive implementation could not be properly hashed, but this could be worked out by for example coinbase transaction would not be left to the arbitrary address generated by the miner but would rather be automatically generated to send coins to contributors of the previous round. Since all clients are aware of who these contributors are or rather what are their addresses everyone should be able to verify if coinbase transaction is correct at the time block is mined.

And yes this should be a new coin. Bitcoin will never accept change of this magnitude. Question is: can we put together a team to develop it? Personally I would join in. My suggestion would be that we spend a lot of time planning before we take on coding.

Name: BlockChainCoin or BCC
Any thoughts? Anyone?