It is by no means an impossible task but it will likely take a long time for someone to come up with a blockchain innovation/feature on par with Satoshi's original idea.
This is very profound.
Bitcoin has a very, very serious, fundamental problem: the absence of anonymity and hence the fact that bitcoins are not fungible. It has other technical problems too (like the limited number of transactions per second). It has also amazingly good properties, but I think the anonymity that is lacking is the most serious problem.
This will bite back one day. But indeed, bitcoin was the first, and has a huge "first mover" advantage especially because of its network effect. Although many altcoins are stupid ideas, some altcoins really have brilliant improvements over bitcoin.
The altcoin scene is the laboratory for crypto, because bitcoin has become "too serious".
What has been said earlier, that bitcoin has a quasi-perfect initial distribution because there was no "greed" the first year or so, can easily be solved by an "altcoin" : instead of starting a new block chain, it could simply fork off bitcoin, hence solving all the issues of initial coin distribution and seigniorage. Ethereum is the first experiment in the altcoin scene of forking off instead of starting new chains.