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At a certain point the n/w knows the miner's i/p. is not it ? Otherwise, how come blockchain.info is giving us the graph ? So, can we implement it in the protocol that after every block is mined, the n/w hash power distribution will be checked and any miner having X%+ will be suspended for next N no. of blocks.
Say, X = 49 & N = 6.
No, the miner must not have a fixed IP. They could use tor a proxy or maybe even fake an IP. Blockchain.info can make the graph because currently the pools dont have to hide their IPs. But with your suggestion they have a reason to hide the IP the block is coming from.